1. Hagia Sophia is a former Orthodox Christian basilica, then an imperial mosque, and now a museum in Istanbul, Turkey. It is considered one of the greatest surviving examples of Byzantine architecture, and it is famous for its massive dome which dominates the skyline of Istanbul. The construction of the original Hagia Sophia dates back to the 4th century, but the building was significantly reconstructed by Emperor Justinian I in the 6th century and has undergone several additional renovations throughout the centuries. In 2020, it was converted back into a mosque by Turkish President Recep Tayyip Erdoğan. Some of the interesting features of the building include its vast interior, with a dome that reaches up to 56 meters in height, and intricate mosaics and frescoes depicting Christian imagery that have been preserved since the 13th century.

2. The opening hours of Hagia Sophia vary depending on the month. In general, the museum is open from 9:00 am to 7:00 pm, but the last entry is one hour before the closing time. The museum is closed on Mondays. You can contact the museum by phone at +90 212 522 1750.

3. As of 2020, tickets to enter Hagia Sophia as a mosque are free, but visitors must reserve their tickets in advance online through the official website. Visitors must also comply with the dress code and remove their shoes before entering. The museum is located in the Sultanahmet neighborhood of Istanbul and can be reached by public transportation, including the tram and bus.