Saint Catherine's Castle

You'll spot this squat little fortress from across the water long before you reach Polruan - a Tudor gun tower plonked right on the headland like some serious medieval security guard. It's tiny, mind you. We're talking 16th century, built by Henry VIII when he was properly worried about French invasions, and it shows. All thick walls and narrow gun ports designed to keep ships at bay.

The walk down is actually nicer than the castle itself. Coastal path gets you there in about twenty minutes from Polruan, cutting through trees and suddenly opening onto the estuary. The real appeal is the setting - you get brilliant views across to Fowey and the harbour below, and on a decent day the light is proper lovely. Inside is fairly bare - stone rooms, a bit of interpretation, nothing fancy - but the gun ports give you that hands-on sense of what it was built for.

History types and photographers will get a solid hour out of it. Young kids might manage thirty minutes before asking to leave. It's managed by English Heritage and free to wander, which helps. The climb back up is steeper than you'd think, so factor that in if anyone's got dodgy knees.

Pair it with walks around Polruan itself or head across to Fowey - both are cracking spots. If you're staying at Tremeer Farm nearby, it's an easy morning trip. The glamping yurts make a solid base for exploring this corner of the Cornish coast.