Coates Portal Sapperton Tunnel 1789

Walk down a country lane near Cirencester and you'll stumble on one of Britain's most underrated industrial monuments - a proper Georgian engineering marvel that most people drive straight past. The Coates Portal is the entrance to the Sapperton Tunnel, an 18th-century wonder dug in 1789 that carried the Thames and Severn Canal under the Cotswold hills. It's not a tourist trap with gift shops and guided tours. You get what you came for: a stone archway emerging from the hillside, the entrance to a tunnel that stretches nearly two miles underground.

The appeal here is straightforward. History buffs will lose their minds over this - it's a tangible link to the canal era when engineers were solving transport problems with muscle and brains rather than explosives. The setting is lovely, tucked into woodland with paths around the portal itself. It's not strenuous, and you can wander the grounds in fifteen minutes or spend an hour if you're photographing or sketching.

Walkers will appreciate the location too. It sits well within day-trip distance from Cirencester, and there's decent countryside to explore nearby. Families with young kids might find it a bit anticlimactic - it's a hole in the ground, really - but older children interested in engineering or industrial history will get something from it.

Free to visit as far as we could tell, no official opening hours to worry about. If you're camping at Cirencester Park or Mayfield Park nearby, it's an easy morning's diversion. Worth the short drive from town.