Holme Fen National Nature Reserve

The iron post sticking up out of the ground near Peterborough looks like nothing much - just a marker, really. But it's actually one of Britain's most dramatic records of environmental change. This is Holme Fen, and that post was driven into solid peat back in 1851. Today it rises about 4 metres above the surrounding ground. The fen has simply sunk.

It's a proper working nature reserve, not a manicured visitor centre with gift shops. You'll find yourself walking across drained fenland that's now grassland and open water, with viewing platforms dotted about. The birdwatching here is legitimate - bitterns, marsh harriers, the full cast. Spring and autumn migrations bring serious twitchers from across the region.

Walkers get the most from Holme Fen. The trails aren't demanding, but they're real enough to feel like you've actually been somewhere, and the flat landscape means you can see across vast stretches. It's the sort of place where half an hour becomes two hours without you noticing. Families with younger kids might find it a bit spare - there's no playground or café - but keen naturalists will want to linger.

Being only 5 to 6 miles from Ferry Meadows and Nene Outdoors campsites, it pairs well with a broader Peterborough trip. Access and exact opening times aren't widely advertised, so ring ahead before you go. Free to visit, and worth the detour if you're into wetland ecology or proper bird spotting.