(CNN) At the forefront of the photo, a diver leaps into azure Spanish skies, arching her body into a streamlined curve.

In the background, a panoramic Barcelona skyline stretches out, punctuated by La Sagrada Familia, Gaudi's half-finished masterpiece of a cathedral, and fringed by distant hills.

Over the course of the Olympics' two-week stint in Barcelona, variations on this eye-catching scene were broadcast on television screens around the world, cementing a spectacular image of the Spanish city in the memories of millions.

The result? Barcelona arrived squarely on the tourism map, transforming from an undiscovered gem to a must-visit European destination: in 1990, there were just 1.7 million overnight visitors, by 2016, there were over 8 million.

Sure, during that time the Spanish city also benefited from the growth of budget flights, a booming cruise industry and increasing word of mouth reports of its many cultural highlights -- but many reckon the successful Olympic stint is what kickstarted the uptake.

But while tourists still flock to Barcelona's Montjuc area to see the view that the Olympics made famous, across the Mediterranean in Greece, many of the venues that were once the glory of Athens 2004 lie seemingly semi-abandoned and forgotten.

They're not alone: In China, some of Beijing's 2008 Olympic venues have been absorbed by nature, weeds growing inside what was once the BMX track.

With a new Olympic city in the spotlight every couple of years, the short-term tourism opportunity and long-term tourism legacy promised by hosting the Games is alluring.

So why do Olympic venues sometimes get abandoned? And how do cities ensure a positive Olympic legacy for both tourists and locals?

Building an Olympic city

The new National Stadium will host the Tokyo 2020 Olympic Games.

Behrouz Mehri/AFP/Getty Images

The Summer Olympics are one of the world's biggest sporting events, and, unsurprisingly, building an Olympic city is no easy feat.

It all starts with a would-be host submitting a bid, outlining how they intend to get their Games off the ground, and how they'll transform their city into a sporting playground.

"These days you need somewhere between 35 and 40 athletic venues to just host the required games for the Olympics," explains Andrew Zimbalist, Robert A. Woods professor of economics at Smith College in Massachusetts, and the author of several studies on the economics of the Olympic Games.

Some of the Olympic venues from Athens 2004 have not fared well.

Milos Bicanski/Getty Images

"On top of that, you need an Olympic village that will house somewhere in the neighborhood of 18,000 people, you need a media village that also requires beds for several thousand people."

In short, it takes a lot of space and a lot of venues.

In that sense, says Zimbalist, a city getting saddled with white elephants post-Olympics is perhaps more likely than not.

The BMX track used for the 2008 Beijing Olympic Games is now abandoned.

GREG BAKER/AFP/Getty Images

In recent years, bidding cities have tried to circumnavigate this issue by planning ahead, devising ways to successfully transform into an Olympic city, and successfully transform back again, whether via temporary venues, or converting pre-existing apparatus.

This isn't just cities being inventive -- nowadays it's pretty much mandated by the International Olympic Committee (IOC), who oversee the Games and the bidding process.

"Image building is extremely powerful," says Christophe Dubi, executive director of the IOC. "But you need a plan. That's what we gauge now, in the dialogue [with host cities.]"

Making the bid

An American tourist presents a ticket at the 2008 Beijing Olympics.

JACQUES DEMARTHON/AFP via Getty Images

Why a destination bids to host an Olympics Games is dependent upon its individual economic, social, cultural and historical factors.

"Cities bid for the Olympics for geopolitics reasons, for media branding reasons, for sponsorship, to track foreign direct investment and talent and so on," says Tony Johnston, head of Tourism at Althone Institute of Technology in Ireland.

While tourism might not be the motivating factor for bidding, hosting a mega event puts your city on show, on a global scale. And such high stakes have, for a long while, come hand-in-hand with high prices.

Andrew Zimbalist, Robert A. Woods professor of economics at Smith College

Some city populations have expressed concerns about the mounting costs. Boston, in the US, and Hamburg, in Germany, withdrew their respective bids for the 2024 games. Boston made the decision after polls indicated a lack of support, while Hamburg pulled out of its bid following a citywide referendum in which 51.6% of residents said they were against the idea.

"We are encouraging the organizing committees to find solutions that are cheaper if they do exist," Dubi tells CNN Travel. "And we really embrace that spirit of creativity, innovation in order to contain the costs."

Dubi says he's confident prices are becoming more restrained.

He also adds that the importance of planning for legacy is true of any major sporting event.

"We are permanently dialoguing with future hosts for 2030, 32, 34 etc," adds Dubi. "What is your long term plan in terms of development for the city and the region? And how can the Games contribute? You have to have a strong plan and the Games as a contributor to make it a success."

London as a case study

The Queen Elizabeth Olympic Park in London was built for the Summer Olympic Games in 2012.

Courtesy The London Legacy Development Corporation

In 2012, right before the Olympic Agenda 2020 was adopted, London hosted the Summer Olympic Games. This Olympic stint didn't offer Barcelona levels of tourism transformation -- perhaps because, as economics and environmental studies expert Victor A. Matheson jokingly put it: "The Olympics aren't going to put London on the map because if London isn't already on your map, you really need to get yourself a new map."

But London's Games did try and prepare for a post-Olympics future. How successfully the city did so depends on who you ask.

The London Legacy Development Corporation was formed a couple months before the 2012 Olympics, with the aim of using "the once-in-a-lifetime opportunity of the London 2012 Games and the creation of Queen Elizabeth Olympic Park to develop a dynamic new heart for east London, creating opportunities for local people and driving innovation and growth in London and the UK."

Peter Tudor, the corporation's director of visitor services, recently showed CNN Travel around the London Aquatics Centre, the swanky water palace purpose-built for the London Olympics' swimming, diving and synchronized swimming events.

It's been a public pool since 2014. On a rainy winter weekday, it was teeming with activity -- from school kids crowding the entryways to serious swimmers doing laps beneath the undulating roof.

"The London Olympics was probably one of the first times people were really thinking about what happens after the Games, lots of cities got to the end of their Games and then asked the question," says Tudor.

The Aquatics Centre cost 269 million to build, and underwent a lengthy, pricey, transformation process to become a public space.

It still hosts official events from time to time: the FINA Diving World Series is scheduled to take place here in March 2020, followed shortly after by the British Swimming Championships.

But for some east Londoners, it's just their local gym -- even if UK Olympian Tom Daley can occasionally be seen catapulting off the diving board.

The London Aquatic Centre is now a public pool.

Courtesy The London Legacy Development Corporation

London's Olympic Park is based in Stratford, in the east of the city, a historically poorer, industrial area. Part of the London Olympic bid was a promise to regenerate this part of the British capital.

Still, this transformation didn't come cheap. The London Stadium was originally pitched at 280 million ($358 million at today's exchange rates) -- its final construction cost was 486 million, and converting it into a venue suitable for West Ham cost an additional 272 million.

And naysayers question whether there was a need for a super fancy helter-skelter, or huge new stadium. Plus, they say, the East End area of the city had been pegged for regeneration whether or not the Olympics came to town.

"If the [British] government had simply provided incentives to encourage that development, then you would have would have gotten much more authentic and organic and deep economic development in that area then anything that you might have gotten from the Olympic construction," says economist Zimbalist.

London's ArcelorMittal Orbit tower -- a piece of public art that doubles up as a slide and viewing platform.

Courtesy The London Legacy Development Corporation

Londoner Julian Cheyne used to live in a housing estate called Clays Lane, knocked down in 2007 to make way for the Olympic Park. Cheyne is the co-founder of a site called GamesMonitor, that views the Olympic project through a critical lens.

"If you are a part of the property industry, then you can make a lot of money out of projects associated with the Olympics," Cheyne tells CNN Travel. "And it means that you get the opportunity to remove people from areas of land which you might have your eye on."

Cheyne was rehoused and received monetary compensation, but he says he had "no desire to move."

He is, in fact, skeptical that the Olympics have any sort of positive impact on tourism.

"It's very difficult to think of any particular benefits that London has had as a result of the Olympics. It was a well known city. It didn't need this boost in order to get tourists to come to it."

"I'm not really a fan of the Olympics at all, I don't think that these major events contribute anything to the cities, apart from a degree of destruction to largely poor neighborhoods," says Cheyne.

The London Legacy Corporation, however, argues the city's Olympics, and ongoing legacy has largely boosted the lives of locals and tourists.

Peter Tudor points to a series of recent high profile sporting events as one example: in 2019, the London Stadium played host to two Major League Baseball (MLB) games between the New York Yankees and the Boston Red Sox. The matches were part of a two year arrangement for MLB to play season matches at the city's stadium -- this year will see the St. Louis Cardinals take on the Chicago Cubs.

The IOC, says Tudor, likes to recommend prospective bidders come and visit the London venues -- to see how legacy building is done.

"We show other nations delegations round on a fairly frequent basis," he explains.

Unexpected tourism

When it comes to an Olympic tourism uptake, almost three decades after divers were filmed catapulting through Barcelona's skyline, the Spanish city's still most often held up as an example of the Olympics' power to transform a city's tourism fortunes for the better.

It's not the only one, though. Turin, which hosted the Winter Olympics in 2006, also saw a boost: Visitor numbers in Piedmont increased from 3.3 million in 2016 to 4.3 million in 2012.

Another Winter Olympics success story is Salt Lake City, Utah, which hosted in 2002.

Utah, once second-fiddle to Colorado as a ski destination, had its profile raised thanks to the Olympics, explains economist Victor Matheson. The exposure led to an increase in the number of skier visits in Salt Lake City (and surrounding area), and more rapid growth than neighboring Colorado, Matheson says.

These success stories might have staying power in the public consciousness, but so too do the abandoned venues; stories on these spots make headlines, populate Instagram and Flickr and inspire think pieces.

While on paper abandoned Olympic infrastructure might seem like a waste, a failure to capitalize on Olympic legacy, oddly, such venues can become a tourist attraction of their own -- albeit a niche, and possibly even illegal-to-visit one.

Sarajevo hosted the Winter Olympics in 1984 and many of the venues are now abandoned.

ELVIS BARUKCIC/AFP via Getty Images

The popularity of "ruin porn" -- artsy photographs of abandoned venues -- can send photographers flocking to the graffiti-strewn bobsled tracks of Sarajevo, or Athens' disused venues.

The IOC, meanwhile, is keen to stress that the venues which appear abandoned sometimes have more to them than meets the eye.

"We are conscious that some venues from past Games are not utilized as fully as they could be," says Bernardo Domingues, media relations manager at the IOC.

"However, too often we see outdated or out of context reports or images of venues from past Games that do not represent the current situation or account for the full picture."

Christophe Dubi, executive director, International Olympic Committee

The IOC points to Beijing's often-photographed BMX track, saying it was always intended as a temporary facility, and photos of the cities Canoeing and Rowing Park, which it says do not demonstrate the facility's full use.

In Rio, the issue, says Dubi, is that temporary venues haven't been dismantled.

Domingues says the IOC is currently conducting a research study looking at the post-Games use of all existing Olympic venues, with results due in early 2021.

Not everything's been perfect in the past, the organization admits, and it says it's learning from this -- pointing to the new Olympic Agenda 2020 reform program.

"The one message that I really insist upon is that we have turned the page. Games bidding and Games organization has been really totally revamped," says Dubi.

Olympic future

The IOC is currently planning for future Olympic Games.

Richard Heathcote/Getty Images

The mission of the modern Olympic Games is to build bridges between countries and celebrate connections -- and offer a stellar fortnight of sporting greatness.

This mission is predicated on the idea that the Olympics sets up shop in a different city every couple of years, opening the world's eyes to the wonders of that particular destination.

Still, some experts suggest that to eradicate fears of disused venues, and as a way of addressing the increasingly fervent question of sustainability, the IOC should abandon the bidding system altogether.

The proposed alternative? A few cities alternate hosting duties at purpose-built, permanent venues. Andrew Zimbalist calls this concept, "the only sensible plan," while Matheson, while admitting that it's not 100% in the spirit of the Olympics, says he would "vote in favor of that -- and in a heartbeat."

Tokyo is hosting the Olympics this summer.

Matt Roberts/Getty Images

The IOC, however, is more interested in an alternative idea that's already being put into practice: giving the Olympic Games a larger footprint -- that is, a region, or even entire country hosting, rather than one city.

The 2026 Winter Olympics, for example, is due to be hosted by Italian cities Milan and Cortina.

And while Tokyo's initial plan for 2020 was to construct new venues on the islands surrounding Tokyo Bay, this idea was rejigged to instead reuse venues from the Games in 1964, build temporary structures that will be dismantled post-Games, and utilize existing structures further afield.

There are 12 venues that are located over five miles from the Olympic village HQ.

This plan comes with an added tourism bonus, as more of the country will be spotlighted.

The rest is here:

The tourism legacy of the Olympic Games - CNN