Flash Lane Aqueduct

You'll find the remains of a Roman aqueduct just outside Waltham Cross, though "remains" is doing a fair bit of heavy lifting here. What survives of Flash Lane is mostly earthwork - a raised bank and channel that once carried water across Hertfordshire towards Roman settlements further south. It's not dramatic, and it's certainly not Instagram-friendly. The engineering is impressive when you think about it, but you're essentially looking at an overgrown ditch.

This appeals most to archaeology enthusiasts and anyone serious about Roman Britain. Families with small children might find it underwhelming after ten minutes. The site is free to access and you can walk it in under an hour, though there's no formal visitor infrastructure - no signage, no cafe, no facilities. It's raw.

The location works well if you're based at one of the Lee Valley parks nearby - either the Sewardstone or Edmonton sites are close enough for an afternoon outing. Theobalds Park is even nearer. You could combine a visit with a walk along the River Lee, which runs parallel to the old Roman route. The aqueduct walk itself isn't strenuous, but it's more of a historical pilgrimage than a scenic ramble. Worth doing if Roman infrastructure genuinely interests you. Otherwise, save your energy for the valley walks.