Gemini Rift (ferrets entrance)

The entrance via Ferrets is a bit of a scramble down Portland's limestone cliffs, but that's half the appeal. Gemini Rift is a proper caving experience - narrow passages, low crawls, and the sort of passages that make you wonder what possessed you to wear your good jeans. You'll need torches, a sense of humour about getting muddy, and reasonable fitness. This isn't a tourist cave with handrails and gift shops.

It's genuinely fascinating if you're into geology or want something beyond the usual seaside attractions. The limestone formations are proper impressive once your eyes adjust, and there's a real sense of adventure that sanitised show caves simply don't deliver. Families with older kids (say, 10 plus) who don't mind tight spaces will find it memorable. Younger children or anyone claustrophobic should probably skip it.

Weymouth's just down the road, so it works well as a half-day excursion from one of the holiday parks - Chesil Beach Lodge Park gets decent reviews if you're staying nearby. Check the website before you go for current access details and safety advice. Tides and weather matter here, so timing isn't casual. Allow a good couple of hours including the scramble down and back up. Free to access as far as I can tell, but bring your own kit.

It's not for everyone, but if you want Portland's geology with genuine purpose rather than postcards from the gift shop, this delivers.