Peel Castle stands on St Patrick's Isle, a small tidal island accessed by a causeway from the town's harbour area. The castle walls, towers, and the ruined round tower of the pre-Norman cathedral create a skyline that is visible from much of the western half of the island. The site has been occupied and fortified since the 10th century, with the current walls dating largely to the 14th and 15th centuries. It is managed by Manx National Heritage and entry is ticketed.
Inside the walls are the ruins of St German's Cathedral — not to be confused with the later cathedral of the same name in the town itself — and several other medieval buildings. The setting on the sea-girt island is atmospheric in any weather, but on a stormy day when waves break against the castle walls, it has a bleakness that feels entirely authentic. Allow at least an hour to walk the walls and explore the interior.