These are one of the Seven Natural Wonders of Portugal, which have been classified as a Property of Public Interest and RAMSAR Site. The Mira de Aire Caves are the largest in the entire country with an extension of approximately seven miles, but you can only visit 1968 feet. Six million visitors have already been there. Out of all the national and foreign school trips from the several education ranks, 15% have visited this natural underground wonder. The Mira de Aire Caves were discovered in 1947 by a group of men who descended on a rope to a small gallery. Only a few years later did they find the true dimensions of the largest caves in the country, which have been since then a place of expedition for speleologists around the world. We now know that the wild caves of Moinhos Velhos, Pena, and Contenda are connected to the Mira de Aire caves forming a great gallery network. During the rainy winters, the waters from this network meet those in the waterfall of Olho de Mira and Regadinho, hence flooding the Mira-Minde Polje.