Gorteen Bay and Dog's Bay: the tombolo beaches

Two beaches, one sandbar

About three kilometres from Roundstone village, a granite headland is joined to the mainland by a narrow spit of sand. This is a tombolo, and it does something genuinely unusual: it puts a beach on each side of the same strip of ground. Gorteen Bay faces east, Dog's Bay faces west, and a single small car park serves both.

What sets these beaches apart is not just the shape of the land but the sand itself. Most Irish beaches are made of quartz, ground down from rock over millennia. The sand here is almost entirely calcium carbonate, made up of the tiny shells of foraminifera, single-celled marine organisms that lived and died in the shallow water offshore and were washed up and deposited over thousands of years since the last Ice Age. Geologists estimate the tombolo is around 90 percent shell material. It is one of only a handful of places in the world where this kind of sand accumulates on land in any quantity.

Why the water looks like that

The pale, almost white sand reflects light very differently to quartz sand, and combined with shallow water it produces the turquoise colour both beaches are known for. On a bright day it can look more like somewhere in the Caribbean than the west of Ireland, which is exactly why photographs of Dog's Bay tend to circulate as if they were taken somewhere else entirely. The water itself is unmistakably Atlantic: cold, even in August, and worth a wetsuit if you plan to be in for any length of time.

The dunes and the machair

Behind both beaches, the dunes carry machair, a low, species-rich grassland that only grows on calcium-rich shell sand along the Atlantic coasts of Ireland and Scotland. It is a genuinely rare habitat, and the area has been the subject of active, community-led erosion control since the early 1990s after the dune system came under serious threat. Keep to the paths through the dunes where you can; the machair recovers slowly.

Wildlife along the shore

Grey seals are a regular sight in the shallow water and around the rocks at both beaches, and out around Inishlacken island a short paddle away, part of the same colony that gives Roundstone Bay its Irish name, Cloch na Ron, the rock of the seals. A local sea-kayaking operator, Move With Nature, runs guided trips out from Roundstone harbour that pass close to the island, giving a different vantage point on the same stretch of coast the tombolo sits on and a decent chance of seeing seals from the water. The machair grassland behind the dunes is worth a second look in late spring and early summer, when it carries wildflowers rooted in the unusually calcium-rich shell sand blown up from the beach. The Geological Survey Ireland has documented the site formally as a geoheritage location, recognition of just how unusual a shell-sand tombolo of this scale is on the Irish coast.

Visiting practically

The car park is small and shared by both beaches, and it fills by mid-morning on a good summer weekend. Arrive early, or be prepared to park further out and walk in. There are no facilities at the beach itself beyond the car park, so bring what you need, water, sun protection, and a windbreak, since there is little natural shelter from the Atlantic breeze even on a calm day.

A short walking loop crosses the headland between the two beaches, roughly three kilometres in total, flat and easy underfoot across sand and machair grass. It is a good way to see both beaches without doubling back, and gives a proper sense of how the tombolo actually works as a landform rather than just two nice beaches that happen to sit close together.

When to go

Summer brings the crowds and the best swimming weather, but the beaches are walkable and largely empty outside July and August. Spring and early autumn are worth considering if a quiet walk matters more to you than a warm swim. Whatever the season, check the tide and wind before heading out; an onshore wind can make either beach considerably less pleasant than the other on the same day, so the choice of which side to sit on is worth making once you arrive rather than in advance.