Costa Rica Guide
The Zona Norte
The Venado Caves
About 30km northwest of La Fortuna, on a paved road near the tiny mountain town of Venado ("Deer"), are the Venado Caves ( 
478-8008; $10, though there may be no one to collect it). This small network of subterranean caverns is quite accessible, provided you aren't afraid of bats and don't mind getting wet. Inside is a spooky and unique tangle of stalactites and smoothed-out rock formations. Some of the passages from cave to cave are so narrow that you should measure whether or not you are going to fit before you begin the crawl. Using the services of a guide is a very good idea – the caves are labyrinthine – and you should bring a flashlight and rubber boots (you may be able to rent them from your hotel if you're staying locally). The caves are closed in the wet season.
Several companies in La Fortuna offer day-trips to the caves, including guide and entrance fee. About three daily buses (ask around as times are always changing) head from San Carlos to Venado (more than 2km from the entrance to the caves) and you can also pick up the bus from the El Tanque intersection 5km east of La Fortuna. More frequent buses from La Fortuna to Guatuso will drop you off at a private farm (owned by Sr Solis). From here to the mouth of the caves it's a walk of several kilometres along a gravel road and marked trail.