This is a very, very famous mosque (arguably the most famous site in all of Mosul next to Nineveh itself) that many Muslims, Christians, and Assyrians visited and still visit today. A whale's tooth, appropriate to Jonah's well-known adventure at sea, is said to be preserved there. Apart from providing spiritual value to many, it also offers a stunningly beautiful view of Mosul from its top balcony. It's exterior lights provide a nice decorative flair to the uniquely designed mosque, particularly at night.
Source: Wikipedia