Located on Battenberg Square in Sofia, the National Art Gallery occupies the historic Ottoman Chelebi mosque and konak, converted into the former royal palace of Bulgaria. The palace, built in two stages during the late 19th century, served as the residence for Bulgarian royalty. After World War II, the monarchy was abolished, and the palace was largely given to the National Art Gallery.
 Established in 1934, the gallery moved to the palace in 1946. It houses a diverse collection, including Renaissance and contemporary art, medieval paintings, and over four thousand icons. The National Gallery for Foreign Art, an independent section, was established in 1985. Since 2015, the 19th and 20th century collections are exhibited together, creating the National Gallery Square 500.
References:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.