The Broch of Gurness is another wonder.
Settlement here began sometime between 500 and 200 BC. At the centre of the settlement is a stone tower or broch, which once probably reached a height of around 10 metres. Its interior is divided into sections by upright slabs. The tower features two skins of drystone walls, with stone-floored galleries in between. These are accessed by steps. Stone ledges suggest that there was once an upper storey with a timber floor. The roof would have been thatched, surrounded by a wall walk linked by stairs to the ground floor. The broch features two hearths and a subterranean stone cistern with steps leading down into it (resembling the set-up at Mine Howe). It is thought to have some religious significance, relating to an Iron Age cult of the underground.:38
The remains of the central tower are up to 3.6 metres (11.8 ft) high, and the stone walls are up to 4.1 metres (13.5 ft) thick.