After fleeing from Bree, Strider and the hobbits avoid the main road and approach Weathertop from the north. At the top they discover a cairn with a message from Gandalf, and see the Ringwraiths approaching in the distance along the road. That night, the Ringwraiths attack their camp in a dell below the summit, stabbing Frodo with a Morgul blade before being driven off.
Weathertop is a hill in Middle-Earth and is the southernmost and highest summit of the Weather Hills. The watch tower at its top overlooks the Great East Road in central Eriador, east of Bree, about halfway between the Shire and Rivendell.
The Atlas of Middle-earth shows the hill rises a thousand feet (approximately 300 meters) above the relatively level lands round about, and with only the lower Weather Hills stretching away northwards, offered a commanding view in every direction.
The cache can be found at:
N 52° 5(2*A).E(D-C)(A-B) W003 0(D+C).(A-1)C(E-A)
A = The number of complete arches (not including gated ones) in the ruin
At the information board in the ruin find the date the castle was abandoned BCDE
The rest of the LOTR series is not far behind but as each cache is a stand alone they are being published separately.
A bookmark of all the caches available can be found to the right of the page.