Tourists can now visit the newly restored underground dungeon at Spain's Alhambra

One of Spain's most visited tourist sites has opened one of its darkest secrets to the public.

Granada's Alhambra palace has unveiled an underground chamber that was once used as a dungeon.

"Alongside the elegant dwellings at the Alhambra there were dark dungeons, housing prisoners," the Council of the Alhambra and Generalife said in a statement.

The underground silo-like prison has been part of a continuous archaeological campaign to restore the palatial Arab fortress.

Its largest subterranean dungeon, known as "Silo-mazmorra Grande del Secano," which the Moors used to imprison captives and sometimes as a grain or spices silo had been suffering from the ravages of time.

"The purpose of the upgrading that is being carried out in this sector is to protect the underground hollow from infiltrations and collapse, and to improve its interpretation for a better understanding of the visitors," the statement said.

More than 20 of dungeons have been discovered on the grounds of the UNESCO World Heritage site.

Located in an area that goes from the Torre del Agua (Water Tower) to the former site of the Abencerrajes palace, the recently opened dungeon is eight metres below ground and includes a 20-metre long gallery.

Access is via a large, circular, 11-metre wide gaping hole in the ground which has the shape of a bottleneck and includes the remains of a stone wall that used to anchor a ladder leading to the dungeon.