[2] In addition, within 100 m (328 ft) of the southern boundary of the SSSI, there is an Iron Age field system, associated hut circles and large middens covering 3 ha (7.4 acres).

It was built to guard the northern, deep water approach, to New Grimsby harbour, although it proved to be badly sited to fire on ships below, or to withstand attack from the landward side.

The round tower of Cromwell's Castle (grid reference SV881159), built on the site of a previous blockhouse, was completed the following year to guard the deep water approach to New Grimsby harbour.

[5] In 1652 the Parliamentary Survey of Scilly reported a row of shallow pits and spoil heaps (grid reference SV884164) following, in part the line of a tin lode.

The thin skeletal podzolic soils and extreme exposure to salt laden winds have led to the development of a wind–pruned, lichen–rich, “waved” maritime heath dominated by heather (Calluna vulgaris).

The heath is species poor with western gorse (Ulex gallii) and some bell heather (Erica cinerea), which becomes dominate on the southern side of the area.

[7][8][9] Peter and Myrtle Ashmore investigated Piper’s Hole in 1993 and amongst the cavernicolous fauna found a springtail new to Britain, Onychiurus argus, a troglophile species known from caves in Belgium, France and Spain.