Newark Castle

The ruins sit on a rocky outcrop above the water, commanding the narrow strait between the Cowal Peninsula and the Rosneath Peninsula. What remains is the four-storey tower house, built in the 15th century, with walls thick enough to stop you wondering how they ever breached the place. The setting is the real draw here - you're looking across to Loch Long with proper Highland scenery on all sides, and the walk to reach it is straightforward enough without being tedious.

It's worth a detour if you're basing yourself at one of the Loch Lomond parks - Loch Lomond Retreat, just over six miles away, puts you perfectly positioned. The castle itself won't consume your afternoon; most people spend forty minutes wandering around and taking photographs. The tower is fenced off (you can't enter), so it's really an exterior exploration. Families with younger children will find it interesting as a stop rather than a destination, though the rocky approach keeps things a bit adventurous. Walkers heading through Argyll will appreciate the spot as a proper waypoint with views that justify the scramble.

Access appears free, though information is thin on the ground - best to phone ahead or check locally in Woodhall. The structure is genuinely impressive for its age, and the fact it's still standing after six centuries tells you something about 15th-century Scottish building standards. Come here for the location and the history wrapped together, not expecting crowds or facilities.