Kara Prison is a vast underground prison built in the late 17th or early 18th century in the city of Meknes in northern Morocco.
It is called Kara (also Qara), after the Portuguese architect who designed and built it, surnamed Cara. He himself was a prisoner who bought his freedom from the sultan in exchange for the work.
Built as an underground labyrinth, it extends for several kilometers and even local legend says that it reaches the city of Taza, something impossible since there are almost 180 kilometers between the two cities.
During the reign of Sultan Mulay Ismail (1672-1727), the first of the Alawite dynasty to rule Morocco, it housed several thousand prisoners, mainly Christians, and it is estimated that its capacity is around 40,000 inmates. Although it did not have doors or cells with bars, it is believed that no one ever managed to escape from it, due to its labyrinthine design.

So far the legend, because the reality is that, although it is true that at some point it could have served as a prison (it is said that there are still inscriptions made by the prisoners on its walls), this underground complex was a warehouse for grain and supplies. In fact, its resemblance to other barns from the same period is obvious.
The tens of thousands of Christian prisoners in the city was probably an exaggeration originating from the accounts of European ambassadors who came to Meknes to negotiate the release of their compatriots. And especially in the stories of Germain Moüette, a French writer captured by corsairs from Salé and who spent eleven years as a captive in Morocco. Seven of them were imprisoned in Mequinez, working on the works of Sultan Mulay Ismail. Rescued by religious Mercedarians, he wrote in 1683 the book Account of the captivity of Mr. Mouette in the kingdoms of Fez and Morocco, where he lived for eleven years.
The number of prisoners would be closer to a few thousand. And also around the same time two prisons were built in the city, one in the Al-Ruwa neighborhood and the other, for Christians, in the Kasbah Qaa Warda.
However, the people of Mequin exploit the legend of the prison for tourist purposes. Among other things, they say that the prison did not have a door, and therefore the prisoners were thrown through a hole on the roof of the building, through which food was also brought to them.
Another legend, this more recent one, assures that a team of French explorers disappeared without a trace when exploring the labyrinth, no less than in the 1990s.
The entrance to Kara’s prison is a ladder found on the kasbah (fortress) of Moulay Ismail, next to the wing of the ambassadors, being able to visit three of the rooms of the complex, made up of a series of vaulted arcades on pillars.
The French colonial rulers closed much of the access (holes) from the surface, due to the many accidents that occurred. They also walled off the access to the labyrinthine corridors, so that today only the three aforementioned rooms are accessible.
The first room receives lighting from holes in the ceiling, the second is accessed through a tunnel in the side of the east wall, and the third is a group of wide corridors interspersed with huge intersecting arches. Recent studies indicate that the extension of the complex would not be greater than the area of the kasbah or fortress under which it stands.
Sources
Visit Meknes / Relation de la captivité du Mr. Mouette dans les royaumes de Fez et de Maroc (Germain Mouette) / Rough Guide To Morocco / Wikipedia