Grassholm (Welsh: Gwales or Ynys Gwales) or Grassholm Island[2] is a small uninhabited island situated 13 kilometres (8 mi) off the southwestern Pembrokeshire coast in Wales, lying west of Skomer, in the community of Marloes and St Brides.

Grassholm is known for its huge colony of northern gannets; the island has been owned since 1947 by the Royal Society for the Protection of Birds, and is one of its oldest reserves.

[6][7][8] Boats sail to Grassholm from St Davids Lifeboat Station and Martin's Haven on the mainland, but members of the public are not permitted to land.

Gwales is the site of a fabulous castle where the severed head of Brân the Blessed is kept miraculously alive for eighty years while his companions feast in blissful forgetfulness, until the opening of a forbidden door that faces Cornwall recalls them to their sorrow and the need to bury the head at the White Mount (the Tower of London).

And because of those fourscore years it was called the Assembly of the Wondrous Head.On 15 July 1945, the cargo ship Walter L M Russ ran aground on Grassholm and sank.