There are two Cairns listed, very close together towards the north part of the moor. One is at SS13234478. As this is clipped by a shallow quarry pit on the south west side, it's pretty easy to locate. As with most Lundy Cairns there is little to see. But the quarry pit pond does add a little photogenic quality to this one though.
The other is at SS13194473. Given limited time I gave this one a miss, but given that the other nearby cairn is easy to locate, I imagine this could be found via that cairn if need be.