One of the best cave tours in Costa Rica is the Venado Cave tour. The Venado Caves are located in Arenal Volcano National Park and it is a proper cave tour that reaches deep inside the land so be prepared to enjoy some spectacular cave exploring. It is advisable to take a water proof camera or if you are willing to risk your mobile phone with the wet conditions in the cave, then put your phone in a zip lock bag.
There is a waterfall inside the caves and there can be some very tight portals to negotiate while traveling through the cave with a tour guide. Be prepared to get wet and it would be advisable to bring a change of dry clothes so you get changed after the tour. The tour guide will provide boots, helmets and front mounted flashlights for you to wear.