Old disused railway between Hemel Hempstead and Harpenden. Mostly now developed to a cycling and walking path. 

http://www.nickey-line.co.uk

Not for the faint of heart or those fearful of exposed trails. Starting from Saddle Mountain trailhead (Highway 67/FR 610/Trail #57 at 8,800 ft) run down the Nankoweap Trail to the Colorado River, and back.  After leaving the rim, the Nankoweap Trail snakes along the red esplanade sandstone. The trail is fairly well marked and cairned until Nankoweap Creek, where it eventually becomes a sandy boulder/scree field that meanders down the creek until the confluence.

English - Circuit de l'Abbaye (circuitdelabbaye.com)