Underi Fort (Jaidurg)

Underi, also known as Jaidurg, is the sister island fort to Khanderi, sitting across the water in the mouth of Mumbai harbour south of the old Prong's lighthouse. Founded in 1680 by the Siddis of Janjira as a naval counterweight to the Maratha-held Khanderi, Underi became a strategic landmark for shipping and the scene of contests for control of these waters. Smaller and quieter than Khanderi, its weathered fortifications and lonely island setting appeal to serious history enthusiasts and adventurous boaters who want to trace the naval rivalries that shaped this coast. The island is undeveloped and access depends on boat availability and sea conditions, so it is very much an offbeat, self-reliant excursion rather than a casual stop. It pairs naturally with a Khanderi trip for those exploring the twin island forts. Reach it by boat from the Thal area. Visit only in the calm October to March season, arrange a reliable boat and confirm timings in advance, and treat Underi as a rugged, historic add-on for the dedicated fort explorer.