Portchester Castle

The walls here are genuinely Roman - built nearly two thousand years ago and still standing on the Portchester waterfront. You're looking at one of the finest preserved Saxon Shore forts in Britain, its massive stone fortifications rising from a spit of land that juts into the Solent. The medieval castle keep sits within the Roman walls, so you're really getting two layers of history in one walk around the perimeter.

What makes it work is the sheer physical presence of the place. The walls are thick, the views across the water proper, and you can actually trace where soldiers stood watching for Saxon raiders. The keep itself - that's the Norman bit from the 12th century - gives you something vertical to explore if you've got the energy. Families will get a decent hour and a half out of it, maybe more if the kids are into climbing the tight spiral stairs and peering through arrow slits.

It's free to wander the grounds and lean against the walls, though there's usually a nominal entry fee if you want inside the keep. Lee-on-the-Solent is just down the coast, which makes it a natural stop if you're already out exploring the shoreline. If you're based at Kingfisher Caravan Park or ScottsHaven - which has stellar reviews - it's barely worth the drive to miss. Not thrilling, but genuinely interesting. Go when the light's low across the water. That's when you feel the age of the thing.