St Catherine's Castle was built in 1536 by Henry VIII, to protect Fowey harbour from French Invasion and as one of several fortifications running along the south coast. This small castle is now in poor condition and is managed by English Heritage.
Blockhouses were added to each side of Fowey harbour mouth for extra support. The blockhouse and bastioned curtain wall are on the tip of a rocky headland at the entrance to the River Fowey estuary, facing Polruan across the water from Fowey. The blockhouse was refurbished to form a two gun battery, below the 16th century fort, during the Crimean War and was used as a practice battery towards the end of the 19th century. During the Second World War an emplacement for a gun battery was dug at the point.
The castle remains overlook the estuary and can be approached by a short path from the beach. They are situated to the south west of Fowey along a footpath from the car park at Readymoney Cove.