Visit Venado Caves!

Four kilometers south of Venado (Spanish for ‘deer’) along a good dirt road, the caves are a popular rainy-day attraction that can be organized as a day trip from La Fortuna, San José and many other cities for US$50 to US$80 per person (including transportation and lunch). Alternatively, visit with your own car, as bus service is inconvenient.
The caves were discovered by chance in 1945 when a farmer fell through a hole in the ground and found himself in an underground chamber surrounded by stalactites (hanging tight to the ceiling) and stalagmites (that might reach the ceiling…get it?). The exploration that followed uncovered an eight-chamber limestone labyrinth which extends for almost 3km. The cavern system, composed of soft, malleable limestone, was carved over the millennia by a series of underground rivers.
The caves get rave reviews from folks fond of giant spiders, swarms of bats and eyeless fish. A guide takes you through the caves, including a few tight squeezes, pointing out various rock formations and philosophizing about what they sort of look like.

Source: Lonely Planet http://ow.ly/i/2V8mU