O'Brien's Castle (Inisheer)

O'Brien's Castle, also called Furmina Castle, is a tower house and National Monument located on Inisheer, Ireland.

Location
O'Brien's Castle is located at one of the island's highest points, in the north of Inisheer.

History
A ringfort once stood on the site, named Dún Formna ("hillfort of the ridge/shoulder", referring to the "shoulder" of land) and dated to between the 5th century BC and 1st century AD.

The castle was built by the Clann Teige, a branch of the powerful O'Brien (Uí Briain) family, in the 14th or 15th century. It was taken by the Ó Flaithbheartaigh (O'Flahertys) around 1582. It was captured and slighted by Oliver Cromwell's army in 1652, during the Cromwellian conquest of Ireland.

Building
The castle is a rectangular donjon (keep). The original doorway was into the first floor, accessed by an external wooden stairs.

The entire first floor was a great hall, with mural stairs up to the parapet. The ground floor was a basement or storage area with three vaulted chambers. The corbel of a bartizan is visible with a human face carved into it.