Cromwell's Castle
Cromwell's Castle is a striking cylindrical artillery tower standing sentinel on the northwestern shore of Tresco, one of the Isles of Scilly, off the far southwestern tip of Cornwall. It is one of the best-preserved and most visually dramatic coastal fortifications in England, rising some 18 metres from a rocky promontory at the narrowest point of the channel between Tresco and Bryher. The tower commands sweeping views across New Grimsby Sound, and its robust, almost monolithic form makes it one of the most photographed landmarks in the entire archipelago. Managed by English Heritage, it is open to visitors and represents a rare opportunity to step inside a mid-seventeenth century military structure that retains much of its original character, including an intact spiral staircase and gun platform at its summit.
The castle takes its name from Oliver Cromwell, and its construction dates to around 1651–1652, following the English Civil War. The Isles of Scilly had remained a Royalist stronghold long after the rest of England had fallen to the Parliamentarian forces, serving as a base for Royalist privateers who preyed on Dutch shipping. This prompted the Netherlands to famously declare war on the islands in 1651 — a conflict sometimes cited as the longest technically unresolved war in history, with a peace treaty not signed until 1986. Admiral Robert Blake led a Parliamentary naval force to take the islands, and once Royalist resistance collapsed, the new regime set about fortifying New Grimsby Sound, which offered a strategic deep-water anchorage. The cylindrical tower was built to mount cannon that could control the channel, replacing an older blockhouse, the remains of which — known as King Charles's Castle — sit on the hillside just above, and which had proven poorly sited for effective artillery fire against ships in the sound below.
The physical presence of Cromwell's Castle is genuinely arresting. It is a tall, round tower of rough granite blocks, weathered to a warm grey-brown by centuries of Atlantic salt air. The walls are immensely thick at the base, tapering only slightly as they rise, giving the structure a solid, purposeful mass that speaks directly of its military function. A low, vaulted guardroom occupies the base of the tower, and a stone staircase winds upward to the open gun platform at the top, where the parapet offers one of the finest panoramic viewpoints in the Scillies. On a clear day the views extend across to Bryher's dramatic Hell Bay, north toward the uninhabited islands of Northwethel and Tean, and south down the sound toward the hub of St Mary's. The wind at the top is almost always present, and the sounds of the sea — the lapping of the channel, the cries of seabirds, the occasional murmur of a passing boat — make it a deeply atmospheric place to linger.
The surrounding landscape is exceptional. The castle sits at sea level on a rocky foreshore, backed by the low, heath-covered slopes of Tresco. Just above it, a short scramble up through bracken and low coastal scrub leads to the fragmentary but evocative ruins of King Charles's Castle, giving visitors a rare chance to see two distinct phases of island fortification in close proximity on the same walk. The broader island of Tresco is famous for its Abbey Garden, a subtropical garden of international renown maintained by the Dorrien-Smith family, who hold Tresco on a private lease. The island is car-free and remarkably quiet, crossed by sandy paths through heathland and pine woodland, with white-sand beaches fringing both the eastern and western shores.
Reaching Cromwell's Castle requires a little effort, which only adds to the sense of discovery. Tresco is accessible by ferry from St Mary's (the main island of Scilly) or by Skybus flights from the mainland to the Isles of Scilly, followed by an inter-island boat to Tresco's New Grimsby quay. From New Grimsby, the castle is a short and pleasant walk northward along the shoreline path — no more than ten or fifteen minutes on flat ground. There are no roads and no vehicles, so the approach is always on foot or by bicycle. The site is managed by English Heritage and entry to the tower itself is free. It is accessible year-round, though the island's boat services operate on seasonal timetables, with more frequent connections in summer. Spring and early autumn offer arguably the best conditions: settled weather, lower visitor numbers than peak summer, and the extraordinary wildflower-studded heathland of Tresco at its most vivid.
One of the more curious footnotes attached to Cromwell's Castle concerns the so-called Three Hundred and Thirty Five Years' War between the Netherlands and the Isles of Scilly. When Royalist admiral Sir John Grenville based his fleet on Scilly and attacked Dutch merchant shipping, the Dutch envoy Maarten Harpertszoon Tromp issued a formal declaration of war — but as the Royalists capitulated before any engagement took place and no peace treaty was ever signed with the islands specifically, the technical state of war lingered unresolved for over three centuries. A Dutch diplomat finally visited Scilly in 1986 to sign a peace declaration, at which point the mayor of the islands is said to have joked that islanders could finally sleep soundly. The castle built in the aftermath of that peculiar conflict still stands, almost perfectly intact, a compact monument to one of the more obscure episodes in European diplomatic and military history — and one of the most rewarding and unexpected sights in the British Isles.