Near the L'Espluga of Francolí is this maze of galleries of over 3 kilometers long which, it seems, were inhabited by prehistoric man. You can take guided walks of the area. Tarragona Cottages http://www.Toprural.Com/cataluna/casas-rurales-tarragona_bd-es-43.htm
I only got know Relliguer Cave a year ago, before that whenever I passed the gate was locked, however, on a local holiday there was free access and I was able to see the place. It is quite tight to get in, dark and ultimately it is a small room (6m2) but what matters is its story. It is said that the place was used to hide Jewish families who came together to pray back in the fourteenth century when only Catholicism was permitted in Spain.
Who would have thought that you’d find a real cave in a parking lot? How should I explain…leading to the Roman Aqueduct, there are three underground reservoirs whose pipes (one of them double) you can explore while scuba diving.
It’s technically not that difficult (relatively speaking), but I wouldn’t suggest it for claustrophobic people or those not looking for a bit of a challenge. If you like this sort of thing, you can do it with a beginner’s level and for only 60 euros.
Personally, I loved it.
Cova de les Gralles is a huge cave carved by water from the torrent of Font Nova, a natural amphitheater enclosed by a dome located about 60 meters from the ground. The tour starts in Capafonts (Tarragona) and takes about 45 minutes to get there. Follow the signs "La Mussara per la font de la Llúdriga" and after 1 km you reach a fork, continue straight. You approach the course of the stream and reach the point with the path up to the Mussara, take this path and after a while you''ll see the stunning natural dome of Gralles. The road dies in the bed of the ravine and you have to trace the course of the river between stone blocks to get to there.
Santa Cova is one of the most popular caves in Serra de Montsant. It's located at 1035m, and is named for a female hermit that supposedly lived there. Inside there is a large stalactite called "Bell," so named because of the echo when struck. Follow the road out of Albarca towards the top of Corbatera rock. Shortly before you arrive, there will be a signpost to the Easter Cove.
Moloner Cove is located in the Serra del Montsant (Tarragona), very close to the Holy Cove. It is slightly off the main road out of Albarca (Priorat) towards the top of the Corbatera rock. Before reaching this point there is a sign indicating the path to the Holy Cove and the Moloner Cove is just before it. You have to look carefully as it is a bit hidden.