Introduction to the Banya Bashi Mosque: The Banya Bashi Mosque was built in 1576 when the Turkish Ottomans controlled Sofia. It has a huge dome with a diameter of 15 meters. The most unique thing about the mosque is that it was built on a natural hot spring. People can even see the water vapor overflowing from the vents on the wall. This mosque is also the only currently functioning mosque in Sofia and a testament to Ottoman rule in Bulgaria.