Duke of Argyll's Battery

You'll find the remains of this 18th-century fortification perched on the banks of the River Leven, just outside Balloch. It's a proper bit of military archaeology - stone walls and earthworks that once protected Glasgow from potential Jacobite trouble. The views across the water are decent, and it's the sort of place that rewards a bit of poking about, especially if you're into old defences and how they worked.

The battery itself isn't massive. You're looking at maybe thirty minutes here if you're leisurely, less if you just want the photos. History buffs will find it worthwhile; families with small children might struggle to stay interested once they've climbed about and got muddy. The surrounding area is lovely for a walk, and it connects well with the wider Loch Lomond landscape.

If you're staying at one of the nearby parks - Lomond Woods or Loch Lomond Retreat are both highly rated and within a few miles - this makes for a quick detour on a wet-weather day or a breather between longer hikes. It's free to visit and there's no set time you need to arrive, which is handy when you're planning around park activities. The location means you're never far from Balloch's proper amenities either, so no risk of being stranded.