Stuck out on the middle of the moor between Jamaica Inn and Brown Willy, this cairn is not the most easily accessible monument on the moor. It can be found by walking up the valley to the left of Codda farmhouse (Nth of Jamaica Inn) until you come to the boundry wall between the two parishes (Altarnun and St Breward) It sits close to the wall on the north side of the valley.
In shape it resembles a boat with a headstone at the upper blunt end. I would estimate it is about 15 yards long and 6 yards wide at the top end.
The Catshole Tor settlement and western Catshole Tor cairn are in the opposite field. From Tolborough Tor head for another gate, just to the west of the angled bit of the field. These gates are very close to each other. This leads you out towards these sites. Note that these four sites are in two separate fields with a fence in between.
Technically most land on Bodmin Moor is 'private' as it is owned by someone, even Downs and Common land. But in reality places like the Tolborough Downs are rarely visited by anyone or anything and as long as you use the normal common sense country code I don't imagine anyone challenging you (don't quote me though as some sort of magic access key!).
This long trip is worth it for this alone. A huge rarity and relatively easy to find (once you get to the general area), especially if you've previously seen a picture of it. You can also spot it from Tolborough Tor.
From Tolborough Tor head for the gate in the angled bit of the field (circa SX171782). Note -the downs were pretty swampy in places when I visited (& more swampy than other upland areas in Devon & Cornwall). The Long Cairn is then 100m away just to the right of the old field wall.
What does a Long Cairn look like? Imagine a small long barrow, made of stones instead of earth, in a triangular shape, typically 17 to 30 m long sometimes with traces of internal structure. At Catshole you can see the large-ish front stone, and from there you can make out what might have been flanking stones, and a small litter of stones in the interior. They are of the fourth millennia BC.
Peter Herring and Peter Rose, in 'Bodmin Moor's Archaeological Heritage' (Cornwall County Council - 2001), map three long cairns on the moor, with three other possibilities. They suggest that the Catshole long cairn is carefully aligned to the east part of Catshole Tor. What I can add is that the cairn in general does align with the west cairn on Catshole Tor, the south cairn on Brown Willy, and the Tolborough Tor Cairn, although the long cairn can only been seen from the Tolborough Tor Cairn, whereas the other three can all be seen from one another.