These are are old natural sources of Selva, which was used by the public during Medieval times.
A stone carved stairway, leads 23 steps underground to the old watermill that used to pump fresh water from the ground. Women went here to wash clothes, and get fresh water to bring home.
Inside the bunker, are two concrete basins that was build in 1837 and 1865. However, we know that the sources was used way before that, probably by pilgrims following the path going to Lluc.