Zumaia

Where it sits. Zumaia is a town of roughly 10,000 people in the province of Gipuzkoa, built where the Urola and Narrondo rivers meet the Cantabrian Sea about 30 kilometres west of San Sebastian and 60 east of Bilbao. The old centre is compact and unglamorous, clustered around the Gothic church of San Pedro, with a small marina in the river mouth and two beaches on either side of a headland: Santiago to the west, broad and sheltered, and Itzurun to the east, short, dark-sanded and hemmed by the cliffs that made this town internationally known among geologists long before anyone came here for a television series.

The flysch. The cliffs at Itzurun expose one of the most complete and legible marine rock sequences on Earth. Over roughly sixty million years, alternating layers of limestone and marl accumulated on a deep sea floor; the Alpine collision that raised the Pyrenees then tilted them until they stand almost vertical, so a walk along the low-tide platform is a walk forward through time at a rate of a few thousand years per step. Around five kilometres of stratigraphic thickness is readable here. Two internationally ratified reference points — the Global Boundary Stratotype Sections marking the base of the Selandian and Thanetian stages of the Paleocene — are fixed in these cliffs, and the thin dark clay of the Cretaceous–Paleogene boundary, laid down when the Chicxulub impact ended the age of dinosaurs, is exposed within a short walk of the beach steps.

On screen. Itzurun supplied Dragonstone's shoreline for the seventh season of Game of Thrones, filmed on this coast in autumn 2016. The tilted strata behind the sand, unlike anything on a British or Irish coast, are the reason the production came, and they were left visually untouched — the castle above the beach is digital, the rock is not.

• The season-seven opener, Dragonstone, uses Itzurun for Daenerys Targaryen's landfall, the walk up the beach and the first sight of her ancestral seat.
• The Queen's Justice, the third episode, returns for the dragonglass cave sequence in which she and Jon Snow examine the Children of the Forest's carvings; the cave mouth is Itzurun, the interior is a set.

The hermitage of San Telmo on the headland above, a small sixteenth-century chapel on a grass shoulder between two drops, is a separate film credit: it hosted the wedding scene in the 2014 Spanish comedy Ocho apellidos vascos, the highest-grossing Spanish film of its decade.

What there is to walk. The Flysch Route runs roughly thirteen kilometres west along the cliff tops from Zumaia to Deba, with a shorter and more popular leg to the Algorri viewpoint and back. From the harbour, small boats run flysch trips in season, which is the only way to see the full height and continuity of the strata; kayak outfits work the same water on calm days. The chapel of San Telmo is a ten-minute climb from Itzurun on a stepped path, and the panorama from its terrace — cliffs receding westward in grey ranks, the beach directly below — is the standard photograph of this coast.

The town itself. Zumaia rewards an hour on foot beyond the beaches. The fortress church of San Pedro, begun in the fifteenth century, holds a Flemish-influenced altarpiece; the Espacio Zuloaga, in the former home of the painter Ignacio Zuloaga on the road to Santiago beach, displays his own work alongside pieces by El Greco, Zurbaran and Goya from his personal collection, and opens on a limited seasonal schedule. The Camino del Norte, the coastal branch of the pilgrim route to Santiago de Compostela, passes straight through town, which is why the bars fill with walkers at odd hours and why beds can be scarce in high summer despite the modest visitor numbers.

Getting there and timing. Euskotren's narrow-gauge line between Bilbao and San Sebastian stops in Zumaia, making the town reachable without a car from either city in about an hour and a quarter; the N-634 and the AP-8 motorway serve drivers, and parking near Itzurun is metered and limited. Tides govern everything: the rock platform that draws geologists and photographers is submerged at high water, and the beach at Itzurun shrinks to almost nothing on a spring tide. Check the table before committing to the day. Late spring and September give the steadiest weather on a coast where summer rain is entirely normal, and the low western light of the late afternoon is what makes the strata read as the ribbed, deliberate-looking structures they appear to be on screen.