A relic from the Spanish Civil War hides in this picturesque Spanish park. There, among the postcard-perfect statues and greenery, is an old bunker buried beneath a thick layer of dirt and grass.

Known as Posición Jaca, the bunker was used by the Republican forces to defend Madrid from Nationalists. If attacked, high-ranking Republicans could seek refuge in the secure subterranean space. Covered beneath feet of soil and confined within the sturdy walls, they’d remain safe from bombs beating the surface above them.

Two hundred people could spend months hunkered down in the bunker, which was surprisingly spacious and equipped with toilets, offices, and electricity. Chimneys poking out of the earth provided ventilation and air circulation, and a communications system would keep the refugees in touch with the outer world.

The park the bunker is in was built between 1789 and 1839 by Duchess of Osuna María Josefa Pimentel, back when the area was part of her estate at Alameda de Osuna, outside the capital, as a lovely garden to host high society parties. During the French Invasion of 1808, the property was handed over to General Agustin Belliard to be used by his troops, but as they retreated the Duchess claimed it back. After her death, the place was administered by her grandson and later his brother, who continued hosting parties, even holding one in 1863 for Queen Isabel II.

The design Parque El Capricho shows English influence, as it includes naturalistic features such as a hermitage house, lilac forests, a lake and several rivers, a maze, and a mock Greek temple. The palace is often used for photo sessions, and in 2016 it was proposed to turn the structure into a museum.