St Mawes Castle

A squat, star-shaped fortress guards the mouth of the Carrick Roads near Truro, built by Henry VIII in the 1540s when invasion threats were taken seriously. St Mawes Castle sits right on the waterfront - you can practically spit into the estuary from the gun emplacements - and it's genuinely one of the best-preserved Tudor castles in the country.

Walking round it takes about 45 minutes if you're thorough, less if you just want the views and a photo. The interior's sparse - lots of stone rooms, narrow spiral stairs, and windows positioned for cannons rather than sightseeing - but that's rather the point. You get a proper sense of its military purpose, not some romanticised castle fantasy. On a clear day you can see across to Pendennis Castle on the opposite headland, which makes for an interesting comparison if you visit both.

Families with older children will find it engaging, especially if they're into military history or just enjoy clambering about fortifications. Younger kids might get restless quickly. The views alone are worth the short detour from Truro, and the little village below the castle has a decent pub and fish-and-chips shop.

If you're basing yourself at Trethem Mill Touring Park - just 2.6 miles away - it's an easy morning or afternoon outing that pairs nicely with exploring the Carrick Roads estuary itself. Go on a fine day; the castle's exposure to weather means it can feel grim and windswept in poor conditions.