Hidden among the alleyways of the Karaköy harbor there is an amazing Ottoman mosque that, in stark contrast to the great height of most Islamic temples in Istanbul, is situated sunken into the earth. For this reason it was dubbed the “Underground Mosque,” or “Yeralti Camii” in Turkish.
The easy-to-miss mosque is accessed from two entrances at street level, which lead to a short tunnel down into the earth. The ceiling is very low and the space is dark, illuminated with just a few lamps and some strident green fluorescents that illuminate the ancient tombs of two Arab martyrs.
The unusual mosque has a storied history. It’s believed that back when the Galata neighborhood was a Genoese settlement, the site was a Byzantine fort. The basement of the fort supposedly held the enormous chain that protected the Byzantine fleet from Turkish attacks by blocking ships from entering the Golden Horn waterway into the city.
After the Ottoman conquest, the subterranean site was used for ammunition storage until, in 1640, a religious leader of the Nakşibendi sect discovered the bodies of two Arab martyrs inside. It’s believed the soldiers participated in the failed Arab siege of Constantinople in the 7th century. It is said the Arab army interred their dead here after the attempted siege, along with valuable items locked in a vault sealed with lead. You can see the graves of the martyrs situated near of the back entrance of the mosque today, and off to the side is a gated room bearing two side-by-side tombs bathed in green light where the bodies supposedly rest.
The subterranean space was eventually converted into a mosque under the auspices of Grand Vizier Bahir Mustafa Paşa in 1757. The building, which for a long time even lacked a minaret, has two entrances at street level that allow access to the site below. When visiting this unusual mosque you seem to move between the shadows as a result of the near absence of natural light. In summer it is not strange to find people napping inside.