Minor Basilica of St. Pius X

The Basilica of Saint Pius X, informally known as the Underground Basilica, is a large Roman Catholic church and minor basilica, located in the town of Lourdes, France. It is part of the Sanctuary of Our Lady of Lourdes. Lourdes is a major Catholic pilgrimage site and the Catholic Church endorses the belief that the Virgin Mary appeared to Saint Bernadette Soubirous there.

The Basilica of St. Pius X is the largest and most controversial of the Domain's churches. It was completed in 1958 in anticipation of the enormous crowds expected in Lourdes for the centenary of the Apparitions. The controversy of this church consists of the fact that it is a modern, concrete building, and it is almost entirely underground.

Source: Wikipedia