The Grutas de San José underground river is a natural cave of incomparable beauty.  Visiting the longest navigable underground river in Europe will allow you to delve the depths of the Earth, sailing calm waters in a boat, admiring the strange rocky shapes that the action of water has moulded over thousands of years, to go back and advance in time at dizzying speed while seeing the growth of stalactites and stalagmites, listening to silence, sensing the murmur of water, hearing the echo produced by a drop of water falling on an underground lagoon, discovering a beautiful landscape that nature has kept hidden since the mists of time until today.