La Fortuna de San Carlos is the beating heart of a part of Costa Rica where several geological wonders meet. Nearby are two stunners: Arenal—one of the most active volcanoes on the planet, routinely bursting with lava and ash—and La Fortuna Waterfall, a majestic chute pouring from a 230-foot cliff deep in a tropical rain forest. Hot springs after hot springs make for relaxing interludes between spectacles and adrenaline-surging activities (zip-lining, hiking, whitewater rafting, horseback riding), and the area's many rustic retreats are blissful places to cap off a day of excursions.