Submarine Centre Helensburgh

The real draw here is HMS Argonaut, a Cold War submarine you can actually walk inside. It's moored on the Clyde near Craigendoran, and yes, it's genuinely claustrophobic in the way you'd expect - narrow corridors, low ceilings, the whole lot. You get a proper sense of what submariners dealt with during those tense decades.

The museum itself covers the history of submarine warfare and development, with exhibits explaining how these vessels worked and why they mattered. It's educational without being dry, though it won't hold young children's attention for more than an hour or so. Adults interested in military history or engineering will spend a good two hours here without noticing the time.

Craigendoran's right on the coast, so you can walk around afterwards and blow away the submarine-induced stuffiness. If you're based at Loch Lomond Retreat - which genuinely has decent reviews - this makes a solid half-day excursion. The other parks in the area are closer to the loch itself, so you'd be driving twenty minutes or so to reach Helensburgh.

Check opening hours before you visit. It's not the sort of place that operates year-round with consistent times. Worth going if submarines interest you or you need a weather-proof activity, but don't expect it to be your main event of the week. It's a rainy-day diversion that happens to be quite good.