The ruins of Fort Purcell, just east of Pockwood Pond along Drake’s Highway, are more commonly known as The Dungeon because of a belowground magazine that looks more sinister than it probably ever was.
First built in the 17th century by Dutch settlers, Fort Purcell was expanded and strengthened by the British in the mid-18th century. Located on about five acres of land, the fort complex was dozens of buildings, including water catchments and storage facilities. It was named for an influential governor, James Purcell, who oversaw construction of a number of the fortifications that once ringed Tortola [1] and the other British Virgin Islands.
The ruins are badly overgrown, and there is no sign marking their location from the road; look for a dirt access road on the hillward side of the highway between Havers and Pockwood Pond. You can park along the highway and walk in, but be careful crossing the road.
Links:
[1] http://www.moon.com/destinations/virgin-islands/tortola