Eagle's Nest is a lookout from the Upper Wyndcliffe in the Wye Valley, just a mile from Tintern Abbey. The views are fabulous on a clear day, details here.
The Wye Valley is a beautiful valley just north of the Severn bridge (M48) and Chepstow. The Forest of Dean is just up the road, containing many other places of interest.
An Ordnance Survey map for the best parking location is shown at this web site. Parking co-ordinates are: N51°40.338', W02°41.378'. From here you can take the slightly longer route (sloping path) to the top, or you could park on the A466 to take the 365 steps to the top. We recommend the path!
The cache is an ammo box and there is lots of tree cover which has thrown off many GPSrs - hence the difficulty rating. We hope it is well hidden so we've enclosed spoiler pictures; you may like to print them out and take them (without studying them!) just in case. THE PICTURES ARE THE HINT.
After you have found and logged this cache, please remember to score/rate it at GeocacheUK.com
Please check out the Geocaching Association of Great Britain offering support for Geocachers in GB.