Sulfur

Sulfur is the 25th clue. It is a Janus clue and was located inside the Hagia Sophia in Turkey.

History
After the Janus branch became the leader of the Ottoman empire, they decided to hide a clue in Turkey. Being the artistic branch, they hid it in the prettiest place they could find...the Hagia Sophia in Istanbul, Turkey among the decorations.

Sulfur
Sulfur is a pale yellow element that is commonly found in nature. Sulfur is commonly used in black gunpowder, rubber vulcanization, the manufacture of insecticides and pharmaceuticals, and in the preparation of sulfur compounds such as hydrogen sulfide and sulfuric acid.