Castle Holm stands on an islet in Loch Strom in Shetland connected to the surrounding land by a causeway which can only be crossed at low tide. Only low walls remain.
Dating to the 12th century, the castle measures 5.5 metres by 6.5 metres, with walls that are around 1.2 metres thick. The ruins stand to a height of around 3.0 metres.
The remains of a possible 12th century stone castle stand on an islet in Loch Strom (W D Simpson 1950). The castle measured 18' 4" by 21' 3", over walls from 3' 5" to 4' 6" thick, At the NW angle the remains are still 10' high. Further east are the foundations of other buildings. The islet is connected to the west shore by a causeway, now ruinous and submerged. (Anderson 1873)