Hidden beneath the Boulevard Père Rémi Sempé in Lourdes, France, is the massive concrete Basilica of St. Pius X, otherwise known as the Underground Basilica.

This architecturally controversial church was completed in 1957 and consecrated a year later by a Roman cardinal. The city of Lourdes is one of the most-visited Catholic pilgrimage sites in the world as it was the area in which the Virgin Mary appeared to a local peasant girl, who would go on to attain sainthood. The staggeringly large subterranean church was subsequently built to house the immense crowds that flood the city on feast dates and other important Catholic holy days. The huge main hall, which measures over 600 feet long (longer than two football fields!), can conceivably house over 24,000 worshippers beneath the ground of the French city. Looking more like the hall of a fantastical Dwarven king than a modern church, the towering arched pillars that line the interior make for an impressive, if drafty, experience.

With no natural light due to its underground construction, and the ultra-modern bare concrete walls, the Basilica of St. Pius X has drawn criticism from many in the church who would prefer a more traditional place of worship at the important holy site. However, most visitors willing to venture into the ground are left awestruck by the site’s angular majesty.