The largest caves in Portugal
They were discovered in 1947, and in 1974 they were opened to the public. There are several halls, each has its own name, like the Red Room, or the Chapel. A river runs through the caves. At the end of the tour you are 110 meters below surface, a lift takes you up at the end of the tour.
Fun for kids: there is an aquatic park right next to the exit of the caves.