The roofless cruciform church on the dunes is what remains of the medieval shrine that grew up around Dwynwen's cell. Through the Middle Ages, pilgrims walked the same beach modern visitors walk, hoping to read their futures in the sacred fish that swam in her holy well. By the 16th century, Llanddwyn was one of the richest religious sites in Wales, kept solvent by the offerings of lovers and the worried. The Reformation ended all of it, and the church slid into ruin. Archaeologists who excavated the site in 2011 and again in 2021 found something the medieval pilgrims never knew: traces of even older buildings beneath the ruined walls, suggesting Dwynwen's followers built on top of something already standing when they arrived.

At the far tip of the island, a short whitewashed tower called Tŵr Mawr - the Great Tower - marks where the western approach to the Menai Strait begins. The tower was adapted from an existing daymark and first lit in 1846, guiding ships into the narrow channel between Anglesey and the mainland for over a century. The pilots who took ships through the strait lived in a tidy row of cottages just inland, weathering Irish Sea storms in a hamlet of three or four families. The lighthouse station closed in 1903; the cottages stand restored, some serving as a small museum to lifeboat and pilot life. A second, taller tower nearby has stood since 1845. Together they make the island's most photographed silhouette: two pale towers above pink Cambrian rock, with Snowdonia rising in the haze across the strait.

What looks like ordinary coastline is anything but. The pillow lavas, jaspers and tortured rocks of Ynys Llanddwyn record a moment 600 million years ago when the floor of an ancient ocean was scraped onto a continental margin. Geologists have been studying this mélange - a chaotic mix of rock fragments crushed together by tectonic violence - for more than two centuries. In October 2022, the International Union of Geological Sciences named Llanddwyn one of the first 100 geological heritage sites on Earth, putting it alongside places like the Grand Canyon and the cliffs of Lyme Regis. The reasoning was simple: nowhere else in the world shows this particular slice of late Neoproterozoic and Cambrian Earth history so clearly, and so close to the path of a coastal footpath.

The Royal Society for the Protection of Birds chose Llanddwyn for its very first reserve in Wales in 1911, drawn by the cormorants, shags and oystercatchers that work the rocks. The whole island sits within the Newborough National Nature Reserve, which drew over 478,000 visitors in 2018 - a remarkable number for a place reachable only on foot. Filmmakers found it too. The 2004 Demi Moore thriller Half Light used Tŵr Mawr as its central image. A scene from the 2010 Clash of the Titans was shot on the same beach. Bryn Terfel sang Cavatina here for a BBC film, calling Llanddwyn 'a very beautiful romantic place' - which is exactly what the medieval pilgrims would have said, in older Welsh.