Clearwell Caves

The moment you drop down into Clearwell Caves, the temperature shifts noticeably. You're entering Britain's largest showcave system - a proper underground cathedral of iron ore mines that go back centuries, with chambers that open up far bigger than you'd expect from the hillside above.

Walking through feels genuinely otherworldly. The caves run deep into the Forest of Dean near Coleford, and the main route takes you past underground pools, past vast red ochre stains on the rock face, past evidence of mining that dates back to Roman times. The lighting is sympathetic enough that it doesn't feel like a theme park, though it's not exactly a caving expedition either - paths are clear, steps are installed where needed.

History buffs will find it absorbing. The mines supplied iron ore for centuries, and you can still see the picks and grooves left by miners working by candlelight. Younger kids enjoy the exploration element, though under-fives might struggle with the uneven terrain and the walk itself. Expect to spend 45 minutes to an hour underground, depending on pace.

Stay at one of the nearby campsites - Whitemead Forest Park and Bracelands are both within a few miles - and you've got proper Forest of Dean access on your doorstep. Combine it with walks, the Wye Valley views, maybe Symonds Yat nearby. The caves work well as a half-day activity that breaks up a longer park holiday nicely.