The Royal Monastery of San Lorenzo de El Escorial is located about 26 miles (42 km) to the northwest of Madrid. It was chosen by King Philip II to commemorate the 1557 Spanish victory at the Battle of St. Quentin and also to serve as a royal necropolis. El Escorial has been the burial site for most of the Spanish kings of the last five centuries, Bourbons as well as Habsburgs.

Its buildings include a monastery, basilica, royal palace, pantheon, library, and rotting room, among others. The Pantheon of the Kings holds remains of 26 Spanish Kings and Queens who were also mothers of Spanish Kings. Royal remains are not immediately interred: they must first be prepared. Initially, the bodies are reduced to bones beneath lime in the “Rotting Room” or “pudridero”. The process takes at least 20 years and often much longer. The Rotting Room is still in use today. Remains of the parents of King Juan Carlos I, who abdicated to his son Felipe VI in 2014, are currently inside the “pudridero” awaiting their eventual transfer to the Pantheon of the Kings. The Rotting Room is off-limits to the public. It is only accessible to the monastery’s monks.

There are two “pudrideros” at El Escorial: one for Kings and another for Princes. Completed in 1888, the Pantheon of the Princes is a group of nine burial chapels. Currently, thirty-seven of the sixty available niches are filled.

On 2 November 1984, UNESCO declared The Royal Palace of San Lorenzo of El Escorial a World Heritage Site.

More Info: en.wikipedia.org