Our verdict
Genuinely under-visited — it isn't signposted and sits well away from any paved road, so you're looking at a walk of up to a mile just to reach it. Worth the effort for the butterflies and gentians if you time it right, but not a spot for a quick pootle.
One of five National Nature Reserves on the chalk downland of Cranborne Chase, eight miles east of Shaftesbury — a deep, forked valley eroded into the chalk, botanically rich and best known for its resident Adonis blue butterflies, seen twice a year in June and August. In early spring it's one of the few places in the country where the rare purple early gentian appears in any number.
National Nature Reserve — one of the country's finest wildlife sites. Open, but stick to marked trails.