Lochmaben Castle

The ruins sit on a peninsula jutting into Castle Loch, about four miles north of Dumfries - not hard to find but easy to miss if you're not looking. What remains is mostly earthwork now: ditches, banks, and the ghost of medieval fortifications that once mattered rather a lot. This was a serious stronghold, built by the English around 1300 and fought over constantly during the wars with Scotland. Climbing up gives you decent views across the water, though the castle itself won't take long to explore - perhaps forty minutes if you're thorough, less if you're not.

Walkers will appreciate it more than casual visitors. The approach involves a decent walk through fields (muddy in wet weather, which in Dumfries & Galloway is most of it), and the reward is largely the walk itself and the views rather than dramatic ruins. History buffs might spend longer reading the interpretive boards and working out which bits are which, but families with young children might find it a bit thin - there's not much to actually do once you're there.

It's free to visit and open year-round. If you're staying at Halleaths Caravan Park or Hemplands Farm nearby, it's worth a morning or afternoon visit to break up the holiday. Combine it with a wander around Dumfries itself - the Braw Town has proper character - and you've got a decent half-day sorted. Don't expect Stirling Castle drama, but for a quiet spot with a bit of Scottish history attached, it does the job.