Meridian Line

The Prime Meridian line runs right through Hertfordshire, and standing with one foot either side of it near Waltham Cross is genuinely odd - you're literally straddling the point from which the entire world measures longitude. It's not a grand monument or anything; more a quiet historical marker that rewards curiosity rather than spectacle.

You'll find yourself in fairly ordinary countryside, which is rather the point. This is where Greenwich's famous meridian actually exists in the real world, away from the crowds and gift shops. The walk here from Waltham Cross takes you through proper Essex-Hertfordshire borderland - nothing flashy, but atmospheric in its own way. History types will find it properly compelling; kids might get the idea quickly then want to move on, which is fair enough.

Timing-wise, you're looking at 20 minutes here maximum, unless you're the sort who likes to contemplate longitude at length. Free, obviously - it's just a line on the ground. The real value comes from combining it with nearby parks. Theobalds Park, just 2.4 miles away and rated strongly, makes a proper afternoon of it - woodland walks, lakes, and actual substance. Fowley Mead Park sits practically on your doorstep at 0.7 miles, handy if you're camped there and fancy a quick historical tick-box before lunch.

Best visited on a clear day when you can see the markers properly. Winter can feel a bit bleak out here, so summer's your friend.