While "number one" is subjective, La Fortuna (Arenal Volcano) is widely considered the top tourist destination in Costa Rica for 2026. It serves as the ultimate "adventure hub," offering the perfect mix of lush rainforests, hanging bridges, and the iconic, symmetrical cone of the Arenal Volcano. Visitors flock here for the world-class natural hot springs, ziplining, and wildlife spotting (sloths are very common here). Close behind is Manuel Antonio National Park on the Pacific coast, which is the most-visited national park in the country due to its unique combination of white-sand beaches and easily accessible jungle trails filled with monkeys. For those seeking "off-the-beaten-path" nature, the Osa Peninsula is the top choice for biodiversity, but in terms of sheer popularity, infrastructure, and the "quintessential Costa Rica experience," La Fortuna/Arenal remains the reigning champion for international travelers and first-time visitors alike.