Dinas Island (Welsh: Ynys Dinas) is a peninsula located in the community of Dinas Cross between Fishguard and Newport, Pembrokeshire, in southwest Wales. It reaches a height of 466' (142m) above sea level at Pen-y-fan, marked by a triangulation point. Dinas Head is strictly the northernmost part of the promontory, where the cliffs meet the sea, but the name is sometimes loosely used to refer to this highest point. Dinas Island is contained within the Pembrokeshire Coast National Park and the headland is under the care of the National Trust.
Dinas Island is a promontory partially detached from the mainland – hence its name; on its landward side it is bordered by a swampy valley cut by meltwater overflow from a glacial lake, melt water freed from reservoirs in the Prescelly Hills by the dwindling ice. This was the same Ice Age melt-water that formed the Gwaun Valley further down the coast.
Plant cover on Dinas Island is typical of a windswept cliff environment, with gorse, bracken and bramble, scrubby trees of hawthorn, blackthorn and hazel, and small oak and ash where there is shelter from the wind. There are also coastal wildflowers such as ling, scabious, thyme, heather, thrift, pennywort, foxglove, and orchids. Bluebells bloom in spring on the eastern slopes.Feral goats at one time inhabited the headland until they were destroyed in 1947.
The Pembrokeshire Coast Path, a 186 miles (299 km) national trail, runs for 3 miles around the peninsula, offering extensive views across Fishguard Bay towards Strumble Head to the south-west, and across Newport Bay to the north-east. This section of the path can be accessed from Pwllgwaelod at its south-western end, and from Cwm-yr-Eglwys at its south-eastern end. Both these locations can be reached from Dinas Cross on the A487, and offer parking and public toilets. A path, suitable for wheelchair access, links the two.