Sion Fort (also Sion Hillock Fort) is a 17th-century Portuguese fortification perched on a small hill at Sion, the narrow isthmus that once connected the islands of Bombay. The fort was built by the Portuguese in 1668 and later occupied by the Marathas and British. The hilltop is now a public park with ruins of the original walls and bastions, and the elevation provides excellent views over the surrounding areas of Dharavi and the Mithi River.
The fort is a peaceful, rarely visited spot in the midst of one of Mumbai's most densely populated zones. Access is on foot up a short trail from the base of the hill. The combination of historical layering — Portuguese, Maratha, and British — and the dramatic views make it worth the short detour. There is no entry fee.