Looming up in the middle of Mount's Bay and connected to the mainland at Marazion via a cobbled causeway, this abbey-crowned island is an unforgettable sight, and one of Cornwall's most iconic images. Initially a Benedictine monastery, and later the seat of the St Aubyn family, it's a must-visit. You can catch the ferry (adult/child £2/1) from Marazion at high tide, but it's worth arriving at low tide so you can walk across the causeway, as pilgrims did centuries ago.
There's been a monastery here since at least the 5th century, but the present abbey was mostly built by Benedictine monks during the 12th century (the same religious order that also constructed the island's sister abbey at Mont St-Michel in France). Highlights of the main house include the rococo drawing room, the armoury and the 14th-century church, but it's the amazing clifftop gardens that really steal the show. Thanks to the local sub-climate, many exotic flowers and shrubs flourish here, and it's all a riot of colour in summer.
Though it's still owned by the St Aubyn family, the abbey is run these days by the National Trust. The house has served many roles down the centuries, including castle and prison. It's thought to have been occupied since ancient times: recent excavations, including an axe head, a dagger and a metal clasp, have proved the island has been inhabited since at least the Bronze Age, but it was almost certainly used by prehistoric people long before. According to some scholars, the island may have been used as a trading post for locally mined copper and tin for several thousand years.
The island's Cornish name, Karrek Loos yn Koos ('the grey rock in a wood'), is thought to commemorate a much earlier time before Mount's Bay was flooded; at very low tides, the fossilised trunks of trees sometimes appear from the surrounding sands.
During winter, access to the island is only possible by boat, but in summer, walking across on the causeway is a magical experience: there's a useful guide to the causeway's opening hours on the website (www.stmichaelsmount.co.uk/plan-your-visit/causeway-opening-times).