Great Isaac Lighthouse, Maritime navigation structure on Great Isaac Cay, Bahamas.

Great Isaac Lighthouse is a circular cast-iron tower, painted entirely white with a black lantern roof, rising 46 m at the north end of the Bimini archipelago. It marks the entrance to the Northwest Providence Channel, 120 km north of Nassau, and stands among the ruins of the keepers' house and cistern. It flashes one white light every 215 seconds, visible 23 nautical miles away.

The lighthouse was erected in 1851 and entered service in 1859, marking the entrance to the Northwest Providence Channel about 120 km north of Nassau. On 4 August 1969 the station was found abandoned by its two keepers, who were never found; the 1969 hurricane record shows Tropical Storm Anna passed close on 1–2 August, causing dangerous weather on the island.

The place is linked to local folklore about a Grey Lady, said to be the mother of a drowned child. Stories of mysterious sounds echoing across the island during full moons have kept the legend alive among residents and visitors.

The site is only accessible by boat from Bimini, which requires planning ahead. The interior stairs have been removed, but the grounds can be walked around, so wear sturdy shoes because the coral terrain is sharp and uneven.

The lighthouse's circular cast-iron tower is painted entirely white with a black lantern roof, and its light flashes once every 215 seconds, reaching 23 nautical miles. The keepers' house, cistern and outbuildings now stand as ruins around the tower.