Harwich Redoubt Fort

The star-shaped brick fortress squatting on the Harwich seafront is one of those proper military relics that actually stops you in your tracks. Built in the 1880s to guard against French invasion - yes, really - the Redoubt Fort is a textbook example of Victorian defensive paranoia, and it's fascinating precisely because nothing ever happened here. The polygonal design with its angled bastions was cutting-edge at the time, meant to withstand cannon fire from every angle.

You can walk right round the exterior, which takes about twenty minutes and gives you a real sense of the scale. The ramparts are still intact, and on a clear day you get views across the estuary towards Felixstowe. History buffs will spend longer examining the construction - the brickwork is meticulous - but families with restless kids might find the exterior loop a bit samey after ten minutes. There's not much interpretation on site, so you'll need to do your homework beforehand if you want the full story.

Harwich itself is just inland, a proper working port town with fish and chip shops that don't mess about. If you're based at one of the nearby caravan parks - Dovercourt Holiday Park and Suffolk Sands are practically on the doorstep - the fort is an easy detour between beach days. Admission details are thin on the ground, but access to the exterior appears free. Give it an hour if you're methodical, thirty minutes if you're just passing through.