Tilbury Fort

A sprawling star-shaped fortress sits on the Thames mudflats east of Tilbury town, all red brick and artillery emplacements staring out toward the river. Built in the 1680s to defend London from invasion - though the Dutch never came - it's a proper piece of English military anxiety turned into stone.

What you actually get is a walk around the ramparts, into casemates and gun positions, across drawbridges over what used to be working moats. The views down the Thames are frankly dull if the light's poor, but on a clear day you can pick out the container ships queuing at Tilbury Docks. The museum bits explain why someone thought stationing 600 soldiers here mattered once. Kids will sprint the perimeter and test their echo in the tunnels for maybe ninety minutes before asking what's next.

Admission costs a tenner or so - it's run by English Heritage - and it's genuinely free to walk the exterior paths if you want the photo without the entry fee. Allow two hours if you're doing the full works; an hour if you're just after the ramparts. Go midweek in autumn when school groups aren't swarming it.

Thamesview Camping is barely three kilometres away, making this an easy morning tick-off before heading to better countryside elsewhere in Essex. It's worth the detour if you're into 17th-century gunnery and don't mind a bit of industrial backdrop to your heritage. Otherwise it's a bit specialised.