The Río Umajalanta, which disappears beneath a layer of limestone approximately 22m thick, has formed the impressive Umajalanta Cavern, of which 4.5km of passages have been explored. Inside are some spectacular stalagmite and stalactite formations and waterfalls, as well as a resident population of vampire bats that have produced an impressively large pile of steaming guano over the years. A guide is mandatory, as it's easy to get lost, and helmets with headlamps are provided.
The exciting descent is moderately physical and you must expect to get both wet and dirty (wear long pants since you'll do some sliding on your bum); there are several parts where you need to crawl and wriggle to get through and a couple of short roped descents. Make sure you have good nonslip shoes on. You eventually descend to a small underground lake and river, which is populated by small, white, completely blind catfish. The ascent from here is fairly easy, as it takes a more direct route.
There are numerous other caverns in the area, most of which are virtually unexplored.
The 8km one-way walk to the cavern entrance takes two hours from the village; it's a completely exposed uphill slog. Most people arrive via transportation with a guide from Torotoro.