Kisimul Castle is probably an early to mid 15th century tower house and enclosure fortress, founded by Gilleonan Macneil. The castle stands on a low rocky islet in Castle Bay, which was occupied in the Neolithic or Bronze Age. The three storey unvaulted tower house, with a 16th century raised parapet, flanks the curtain wall. Standing against the inner walls of the small courtyard were, a feasting hall, a chapel, a tanist's house and a gokman's house. A late 16th or early 17th century gateway replaced the two 15th century entrances and outside beside the original landing-place, are the foundations of a galley and crew house. Abandoned in the 18th century, the ancillary buildings and the curtain wall were partly dismantled. The MacNeils sold Barra in 1838 but Robert Lister MacNeil repurchased the estate in 1937 and restored his ancestral castle.