Known among the public with nicknames such as "The Red Castle" and "The Red School", this gigantic building is without no doupt one of the most beautiful and dominant structures on the Golden Horn. Designed by the Ottoman Greek architect Dimadis in 1883, the building was constructed with an eclectic mix of ancient styles. The total cost of this building was 17'210 Ottoman gold liras, an enormous sum for that period. Despite its function as a school, the building is often referred to as "the 5th largest castle in Europe" because of its castle-like shape. The Phanar Greek Orthodox College is the oldest surviving and most prestigious Greek Orthodox school in Istanbul. Established in 1454 by Matheos Kamaryotis, it soon became the school of the wealthy and prominent Greek families in the empire, and many Ottoman ministers and Wallachian princes were graduated from it. The large dome at the top of this building is used as an observatory for astronomy classes and has a large antique telescope.