The Bibi-Heybat Mosque sits on a hillside south-west of the city, overlooking the bay and the Bibi-Heybat oil field — one of the oldest productive oil fields in the world, with derricks still standing in the water below. It is a major Shia pilgrimage site, built around the tomb of Ukeyma Khanum, a sister of one of the Twelve Imams who fled here in the eighth century.
The architecture is broadly Shirvan-style with three domes and two minarets, and the interior is decorated with ornate mirrored ceilings and elaborate ironwork. It's about a twenty-minute drive from the centre of Baku and worth combining with a stop at the Bibi-Heybat oil field — the surreal juxtaposition of pilgrims and pumpjacks is one of the city's stranger sights.