The distance between the Disgwylfa cairn and the various “piles of stones” marked on the map seems too long, despite the easy walking involved. One of the piles looks like a candidate for an older cairn, although Coflein doesn’t agree. By contrast, I pass what turns out to be the Nant yr Ychen cairn with barely a glance. There is no sign of an obvious mound and the pile marks the junction of footpaths. There are yet more terrific views though, except to the north where my day’s highpoint, Pen Twyn Mawr, blocks off everything beyond.
A cairn of uncertain age, but Coflein suggests it may be prehistoric:
Situated on the summit of the ridge above the Nant yr Ychen and the Grwyne Fechan. Stone built and roughly circular on plan, measuring about 8m in diameter and up to 0.5m in height. Probably a routemarker, but some stones eroding out of the vegetation suggest that it could be older than post medieval. The cairn has a deep hollow, presumably the result of antiquarian investigation or robbing. The resulting spoil now forms the walker's cairn that overlies the south-east side.