Middleholm or Midland Isle is a small diamond-shaped island lying between Skomer Island and the Deer Park promontory fort, separated from them by fierce tidal races. The island measures approx. 370m east-west and the same north-south. It is difficult to land on given its steep rocky sides, yet it preserves remains of settlement.

On the northern side of the island (at SM 746 092) is a rectangular embanked enclosure occupying a more level saddle of ground against the sea cliffs. The enclosure measures 35m x 29m, and only has earthworks on the landward side. There are two circular house platforms within the enclosure, sited alongside the 'rear' boundary away from the cliff edge. The western hout is oval and measures 9m x 7m. Running south from above the enclosure is a north-south median bank measuring 200m, dividing the island. The 2011 LiDAR survey of the island does not reveal any other traces of built settlement here. These features can be compared to the extensive traces of abandoned ancient settlements and field systems on Skomer Island (NPRN 24369), and may also be later prehistoric in date although a medieval or later date cannot be discounted without field inspection.

The island was described quite fully by R. M. Lockley and D. R Saunders in Nature in Wales Volume 10, No. 4, for September 1967 (pp. 146-150), where further useful information on the geology, human settlement, place names, vegetation and wildlife is provided. A closer examination of the settlement enclosure was provided: '...the presence of two distinct stone and earth buildings (foundations) on the flatter portion on the north-west side of the island, elevated but sheltered from all winds except those from that quarter. Tucked up under the outcrops protecting them from the east are two rooms, side by side; one still has two large door stones on edge to indicate the entrance... One day we scarped away the debris from the entrance doorway... and found very little beyond a few cut sheep bones, probably thrown aside by recent rabbit-catchers...To the south-west of the houses (or whatever buildings they may be) is a distinct wall or ha-ha, containing nearly level land, as if at one time it had been a small cultivated field, or sheep pen.' (ibid., 148).

T. Driver, RCAHMW, May 2015