Many millennials will travel the world this fall, visiting some under-the-radar destinations along the way. CheapOair recently reviewed its data to unveil eight places that are trending up when it comes to younger travelers.

Millennials heading to Liverpool this fall will surely find fewer crowds than in London. Plus, the maritime city is gaining momentum among younger travelers thanks to buzzing nightlife, scenic outdoor spaces and loads of cultural attractions, including The Beatles Story museum.

Americans looking for an international destination relatively close to home should consider Montreal. Those planning an autumn visit are likely to save significantly on flights and accommodations, leaving them more spending money for attractions, food and seasonal events.

There are plenty of weird and wonderful reasons to visit Portland this fall, including art, music, food and an array of outdoor activities such as hiking and biking. The fun begins as soon as you land at Portland International Airport at it's among the world's most unique.

Average airfares from the U.S. to Phuket, Thailand drop off dramatically in September and October, according to CheapOair, and the sun-kissed resort island is only getting more popular. Visitors should be sure to bring their appetite and bathing suit as the cuisine and beaches here are unrivaled.

Ann Arbor is best known as the home of the University of Michigan so autumn visitors should be sure to tour campus and cheer on the Wolverines at "The Big House," which is the largest stadium in the country with a capacity exceeding 107,000. What's more, Ann Arbor, also known as "Tree Town," is among the top Midwest destinations for fall colors.

Home of the Terra Cotta Army-a collection of life-size sculptures buried with China's first emperor, Qin Shi Huang-Xi'an is a fantastic fall destination for history buffs and culture seekers. Average airfares from the U.S. exceed $1,000 in September but drop to just over $600 in October, based on CheapOair's data.

The City of Angels is a no-brainer for millennial travelers, especially ones that love sports. Beach bums, foodies and visitors who are passionate about music are also in for a memorable experience.

Lisbon is beginning to catch on as a kid-friendly destination but is also a big hit with millennials, attracting more of the generation's travelers from the U.S. than ever before, according to CheapOair. The Portuguese capital stands out for many reasons, including its unique architecture, which is at its best in the Alfama neighborhood.