Gypsy Lane is now inaccessible to traffic, but apparently once formed part of the Turnpike road from London to Birmingham (toll roads in the 18th Century). The lane - a public footpath - takes you between two fields owned (currently) by the Warner Brothers Leavesden Studios (see if you can spot some intriguing sets) and links a busy roundabout with Abbots Langely village. It's a popular dog-walking / running / cycling route, so be on the look out for muggles.
The cache is a magnetic micro one, and you will need to reach up to get it!
Parking is available close by, across the busy main road.