The cache has been placed to give a break from endless motorway driving. It is an unashamed cache and dash. You are looking for a small beaker, sprayed black. Room for small swaps only.
To get to the cache, exit the M25 Junction 20 roundabout and head towards Aylesbury on the A4251 towards Kings Langley. A hundred yards or so up the road, turn left into Langley Lodge Lane. If you miss the lane, there is a roundabout further up the road so you can turn round and have another crack at it! There is a layby right by the cache, so it should be possible to turn round in the lane quite easily. Enjoy the other drivers whizzing past on the slip road. The cache also enjoys panoramic views over the valley towards Nash Mills, the canal, mainline West coast railway, M25 viaduct and the only wind turbine in the 'Greater London' area. Mmm, Lovely!
You could easily combine this cache with Motorway Mayhem M25 J19 and also with HM4 - A gate to nowhere (Herts), which are both also cache and dashes, coming off at J20 and re-joining the motorway at J19 or vice versa. If you want to take a real break, Kings Langley has a good selection of shops, pubs, take-aways and all the usual amenities. There is also another cache up there: Hidden Sword not-so-virtual cache