Yeraltı Camii
Istanbul Province, Turkey
The Yeraltı Mosque (Yeraltı Camii, lit. 'Underground Mosque') is a mosque located in the Karaköy part of the Beyoğlu district in Istanbul, Turkey. The mosque's name is derived from the fact that its prayer hall and main features of it are all underground. It is sometimes known as Kurşunlu Mahzen, as it was a place where the belongings of captured Umayyad warriors were sealed away with molten lead.
Mosque data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).