When you're on Tresco, take a walk above Old Grimsby to the remains of this small fortress. The ruined King Charles's Castle is managed by English Heritage, and is one of those wonderful little sites that's free to visit at “any reasonable time during daylight hours”. It's accessible only on foot, and is well worth the walk for the views as well as the glimpses into garrison life.
Despite its name, King Charles's Castle is actually a Tudor fortress, one of many built around the Cornish coast to guard against French invasion. It was built here, high above Old Grimsby on Tresco, to protect the narrow channel towards St Mary's; however, it soon turned out that its position wasn't as helpful as first thought. The guns would have had to be pointed at such an angle to actually reach any French ships, that the cannonballs would have simply rolled out before they could be fired.
However, the garrison limped on, and the castle continued to be used and strengthened. It was a Royalist stronghold in the Civil War, hence its name. It proved no problem for the Parliamentarians, who simply landed on the other side of the island and took control from there. To add insult to injury, stones were taken from King Charles' Castle to build Cromwell's Castle (lower down, with more effective sight lines).
Today, you can still spot intriguing details of the soldiers' lives among the ruins. You enter through the guardroom, where an arched doorway leads into what once was a large hall. There are two large fireplaces, and you can still make out that one had a bread oven. The smaller rooms were probably sleeping quarters. Another doorway leads to the gun platform. Despite its state, it's easy to build up a mental picture of the old fort.
Today, the elevation that was ultimately the castle's downfall is now its selling point. Walk up here to enjoy the views and tranquillity, as well as to explore the old ruins.
