St Michael's Mount is in Mounts Bay, Cornwall and is now owned by the National Trust. It is a castle on top of a small island. The island that St Michael's Mount sits on is connected to the mainland by a causeway that appears at low tide. The town of Marazion is on the shore beside it. During its recorded history it has been a priory, fortress, a place of pilgrimage, the home of the St Aubyn family from 1659, and now open to the public by the National Trust.
St Michael's Mount is an island for most of the day, but for a few hours each day when you can walk across the causeway to the island. Ferry boats run regular services to the island when the tide cuts off the causeway.
Edward the Confessor granted the mount to the Benedictine monks from Mont St Michel in France, and by 1135 they had built a priory on the summit of the mount. They also constructed a harbour and causeway. Henry V granted it to the Abbey of Syon in Twickenham. From the 12 century it was the site of a number of military sieges, as well as a place of pilgrimage.
Henry Pomeroy captured The Mount on behalf of Prince John, in the reign of Richard I. John de Vere, 13th Earl of Oxford, seized it and held it during a siege of twenty-three weeks against 6,000 of Edward IV's troops in 1473. Perkin Warbeck occupied the Mount in 1497. Humphry Arundell, governor of St Michael's Mount, led the rebellion of 1549.
Then Henry VIII sequestered it on the dissolution of the monasteries. At that point in its history it became a fortress. It was threatened, but not actually attacked during the Spanish raid on Mounts Bay. During the reign of Queen Elizabeth it was given to Robert Cecil, Earl of Salisbury, by whose son it was sold to Sir Francis Basset.
During the Civil War, Sir Arthur Basset, brother of Sir Francis, held the Mount against the parliament until July 1646. The commander of the Parliamentarian forces that captured the mount during the Civil War was Colonel John St Aubyn. He purchased it from the state at the end of the Civil War in 1659. It is one of his descendants, Lord St Levan, still lives there.
Lord St Levan gave St Michael's Mount to the National Trust in 1954, but still lives there. Today around half a million visitors a year visit the site. It can be reached by causeway at low tide, or from a passenger ferry at high water.