Castell Trefynwy/Monmouth Castle

The ruins of Monmouth Castle sit right in the heart of Monmouth town - a Norman stronghold that's seen better days, frankly, but still commands respect. What you're looking at is mostly the gatehouse and curtain walls, chunks of red sandstone that've weathered seven centuries reasonably well. Henry V was born here, which is the main claim to fame, though there's precious little interpretation on site to tell you much about it.

It's a free wander, and honest truth - you'll spend about thirty minutes poking around unless you're genuinely keen on medieval military architecture. Kids will get a kick out of climbing on walls and peering through arrow slits, but they won't be entertained for hours. History types will find it interesting enough as a stopping point rather than a destination in itself. The castle sits bang in the middle of Monmouth, so you can combine it with a proper look round the town's Georgian streets and riverside walks without any bother.

If you're based at one of the local campsites - Doward Park or Bracelands are closest at around three miles out - this makes for an easy afternoon jaunt. The Forest of Dean and Wye Valley walks are the real draw for that area, and Monmouth Castle works as a town-day activity when the weather's dodgy or legs need a rest from serious hiking. It's the sort of place that slots neatly into a broader holiday rather than justifying a special trip on its own.