While not one for the claustrophobic, if crawling through narrow rock crevices, swimming in eerily-lit underground pools and scrambling through pitch black caves sounds like your idea of an adventure, grab a headlamp and a crash hat, and head underground. Caving is not only a challenge, but a chance to discover some otherworldly scenery. Explore the many levels of chambers underneath residential areas during a small-group Budapest caving tour. Swim into a cave ancient Mayas believed was a portal to the underworld with a visit to the Actun Tunichil Muknal Caves from San Ignacio. See an underground river and crystalline formations on a Rio Secreto Underground River and Crystal Caves tour. Go rafting and tubing over underground waterfalls on a tour of the Black Water Waitomo Caves. Let the lights of thousands of glow worms enchant you during a trip to the Te Anau Glow Worm Caves.