The small isle of St. Michael's Mount, accessible by foot when the tide is out, has been home to a priory, castle and stately home.

Bernard of Le Bec, Abbot of Mont St. Michel in Normandy, built the Benedictine Priory of St. Michael's Mount in 1135. There is a similarity between the two islands, although St. Michael's Mount could never match the scale and grandeur of Mont St. Michel, and was only ever a dependency of the Norman Abbey. When King Henry V declared war on France in the early 15th century, he seized St. Michael's Mount for the crown as an alien priory, and by 1424 all links between the two priories had been broken.

The conflicts with France and Spain and the threat of attack necessitated the need to garrison the Mount, although the only forces it came up against were domestic rather than foreign. The last major period of military activity was during the Civil Wars (1642-51) when the Mount was held for the Royalist cause. After the war the castle lost its military function and instead became the family home of the last military governor of the Mount, Colonel John St. Aubyn.

It is important to check local tide times if you wish to walk across the causeway to the castle. During the summer, a ferry service is available to and from the Mount at high tide. There is a steep climb to the castle at the top of the Mount. Unsuitable for prams and pushchairs. Passages in the castle are narrow, so some delays may occur at the height of the season.