Will it be open? Prayer, Mass and Shabbat closures
Short answer: Working mosques close to tourists around each call to prayer and on Friday at midday; cathedrals close for Mass and the papal audience; synagogues close for Shabbat and Jewish holidays. Prayer times and Shabbat follow the sun, so the closed hours move every day. Pick a site to see the open windows on your date.
Blue Mosque
Today: Open to visitors 08:30–12:00, 13:30–15:15 and 16:10–17:40; closed for the noon prayer, afternoon prayer and sunset prayer.
Hagia Sophia
Today: Open to visitors 09:00–19:00.
Süleymaniye Mosque
Today: Open to visitors 09:00–12:00, 13:30–15:15 and 16:10–17:40; closed for the noon prayer, afternoon prayer and sunset prayer.
Sheikh Zayed Mosque
Today: Open to visitors 09:00–21:00.
Sultan Qaboos Mosque
Today: Open to visitors 08:30–11:00.
Hassan II Mosque
Today: Guided tours only, starting at 09:00, 10:00 and 15:00.
Prague Jewish Quarter
Today: Open to visitors 09:00–16:30.
Old-New Synagogue
Today: Open to visitors 09:00–15:15; closed for the start of Shabbat.
Mezquita of Córdoba
Today: Open to visitors 08:30–09:20 and 10:00–18:00; closed for the morning Mass.
St Peter's Basilica
Today: Open to visitors 07:00–19:00.
How we calculate it
Each call to prayer is set by the sun: dawn and night by how far it is below the horizon, noon by when it is highest, the afternoon prayer by the length of a shadow, and the sunset prayer by sunset itself. We compute these for each date with the method the local religious authority uses, then apply each site's own rule for how long before and after the call it shuts its doors to visitors. For synagogues, Shabbat begins 18 minutes before sunset on Friday, and holidays follow the fixed Hebrew calendar.
Each site's rule comes from its official page or a dated on-site check, shown on the page. Rules do change, so the date we last checked is listed next to each one.