Approximately halfway between the gates on the Great Ravelin, there is a fortress guardhouse facing the Stambol Gate. Today, it houses the Gallery of the Museum of Natural History, which occasionally organises exhibitions of its collections of minerals, flora and fauna from around Serbia. The building was erected in the third decade of the 19th century for the needs of the Turkish fortress garrison. As the guard headquarters, it was supposed to protect the main entrance to the fortress. It is one of the few buildings from the final period of Turkish rule. It has an interesting facade, designed in the spirit of classicism but adapted to the traditions of Balkan architecture.