You've got vacation time accumulated, but where to go? Although hard to believe, a recent study found that many Americans don't use manyor anyof the paid vacation days they're offered.

The new year offers opportunities to venture out to one of the dozens of spots experts say are hot right now. Industry experts have plenty of suggestions about where you should go, both internationally and domestically.

Whatever your choice of destination, one thing is certain: You won't be out there alone.

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The U.S. Travel Association is forecasting that there will be 2.1 billion domestic trips in 2015, with more than 78 percent being leisure travel. The organization also expects 75.1 million international travelers will be coming to the United States this year, about a 4 percent increase over 2014.

International outbound business travel from the U.S. in 2015 should increase by 6 percent, "despite the overall weaker economic outlook overseas," said Mike McCormick, executive director of the Global Business Travel Association. He said overall U.S. business travel spending will increase to 6.2 percent to $310.2 billion.

And, thanks to factors such as falling unemployment and a strengthening dollar, the ITB World Travel Trends Report 2014-2015 forecasts a 3 percent increase in overall North American outbound travel in 2015.

Many of those restless souls are expected to be millennials. Hotwire found that approximately one-third of that age group intend to travel more this yearand are a budgeting a total of $226 billion for their domestic and international adventures.

"This mentality is exciting to see and we anticipate that their travel intentions will have significant impact on the industry in the coming months," said Henrik Kjellberg, president of the Hotwire group, told CNBC via email.

Separately, the over-50 group may spend at least $120 billion on leisure travel, according to data from the AARP, and plan to take at least four trips in 2015

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Vegas, Vietnam or Romania? Hot travel sites for 2015