Prison de Kara

Constructed during the early 18th-century during the reign of Sultan Ismail bin Sharif, the Kara Prison (or Habs Qara) is a vast subterranean prison in the city of Meknes, Morocco. Its most unusual feature is that it lacked doors and bars, but it's believed that no one ever escaped.

Its inescapability despite lacking bars and doors was due to its complex labyrinth-like design. It was named after a Portuguese prisoner who was granted freedom on the condition that he constructed a prison that could house more than 40,000 inmates.

The entrance is located in Ismaili Qasba, but the labyrinth goes on for miles. Some believe it's roughly the size of the city itself, while others say it reaches the city of Taza, over a hundred miles east of Meknes. According to legends, a team of French explorers attempted to discover the vastness of the prison and never returned.  

Each hall of the dungeon contained several corridors, which led to another hall, into another, then into another.

As time went on, the prison was discontinued and was utilized as a storage facility for food. Today, a portion of the former prison is open to the public, but its true extent is still unknown.