1. Stone-built roundhouse, measuring 3.1m internally, with an entrance facing south-east. The walls are constructed of boulders ranging from 0.2m to 0.3m in size. Off-centre within the south-eastern quadrant of the roundhouse, is a square setting of stones, c. 0.6m by 0.6m. Some of the stones used in its construction appeared reddened, possible as a result of burning, suggesting that this may have been a setting for a hearth. The roundhouse wall abuts a field boundary to the north and south of the entrance.

O Davis, RCAHMW, 21/01/13

2. The structure was recorded during a field visit on 14th October 2016 by T. Driver and L. Barker, RCAHMW. Re-investigation now suggests that the structure is rectangular, not circular. A number of upright facing stones of the wall can be made out on the south side which describe a straight line, but this line is confused in places with spread and tumbled stone. Right angles can be discerned in the structure which would now seem to represent a rectangular building of uncertain age. In the dry conditions at the time of the visit the clear stone setting with fire-reddened stones previously seen could not be identified with certainty.

T. Driver, RCAHMW, 17/10/2016

3. Reassessment of the structure during fieldwork on 21-22nd Oct 2019 suggests an oval or rectangular structure, aligned generally east-west. The south wall externally is 5.8m long, the north wall 5.5m long. The external width of the building is 4.7m. The eastern end of the building is lost in a more open tumble of loose stone, potentially the site of the original entrance. The walls vary in width between 1.1-1.3m.

4. On the 21st-22nd October 2019, CHERISH Project staff from the Royal Commission and Aberystwyth University successfully undertook two days of fieldwork, survey and evaluation excavation on Grassholm Island with the permission of the RSPB and NRW. Royal Commission staff had previously made two visits in modern times, in 2012 and 2016, both being day visits lasting only a few hours accompanying RSPB staff on their annual autumn trips to free fledgling gannets from plastic debris (Davis 2012; Davis and Barker 2012). The two-day visit in October 2019 allowed considerably more time for site reconnaissance, survey and record enhancement than had been possible on previous visits; all 5 of the Fieldwork Objectives listed in the WSI (see below) were achieved.

The main achievement was the excavation of a small (2.55 x 0.8m) evaluation trench across House 1 (NPRN 418264) to investigate the character and survival of the building and attempt to reach a floor level for the recovery of datable material. In practice the trench was excavated 0.34m down inside the building and 0.23m outside before the water table was reached. However probing established that the likely internal floor survived at 0.65m below the modern land surface. As the wall stones protrude only 0.14m above the modern surface the excavation appears to confirm that the standing archaeology of Grassholm is being actively buried by the nest-building activities of the gannets. More detail is provided below.

T. Driver, L. Barker., D. Hunt 2019