Tucked within the lush, tropical Sierra Nevada de Santa Marta mountain range, Colombia's Ciudad Perdida ( or “Lost City”) is among the great ancient ruins in South America. There's no easy way to reach Ciudad Perdida; visiting this hidden settlement demands a four-day mountain trek with numerous river crossings. The payoff is well worth it: Just a few dozen intrepid travelers reach this expansive site with its terraced hillsides and circular plazas every day, meaning you'll get to enjoy it almost uninterrupted.

Only a handful of Santa Marta-based tour operators are certified to guide visitors to the site, still cared for by the descendants of the Tairona people who built the settlement centuries ago.