The Río Subterráneo " las Grutas de San José" is a natural cave with an incomparable beauty. You can visit the more length navigable river in Europe, it will allow you to enter in the depths of the Earth furrowing in boat calm waters, to contemplate the capricious forms of the rocks that the action of the water has molded during thousands of years, to back down and to advance in the time while you imagine the growth of stalactites and stalagmites, listening to silence, to perceive the murmur of the water, to hear the echo that produce to fall a drop of water on an underground lagoon, discover a beautiful landscape that the nature has maintained hidden from the night of the times to the present time.