Located in the heart of Mumbai Harbour, south of Prong's Lighthouse, is the Island of Underi. Also known as Jaidurg, this fortified island was founded in 1680 CE by Kahim of Siddhis. Comparatively smaller to Khanderi, a sister island, both the islands were landmarks for shipping vessels.
Underi also houses a cave with interesting carvings; the underground chambers were home to prisoners during British rule. aAlthough it's presently in a dilapidated state, the island is open to locals and tourists. The only way to reach the island is through a jetty that functions only during low tide.