The Wern is a seven acre nature reserve in east Monmouthshire, managed by Gwent Wildlife Trust, containing a mix of open woodland, rough grassland, clumps of bracken and a small area of heath, on the northeast side of a low hill, Craig-y-Dorth, which is still high enough to offer good views northwards, across the River Troddi towards Monmouth, though the town itself is hidden behind a wooded ridge. This location is a few miles west of the Wye valley, accessed by a country lane through the village of Caer Llan, off the B4293. Other features in the reserve include an outcrop of coarse-grained sandstone, many mossy sandstone blocks, a marshy area and several ancient dry stone walls, now overgrown and partly collapsed.
The reserve is generally shady, so conditions are ideal for ferns, liverworts, lichens and mosses. All wildflower species found here are common, while wildlife is mostly restricted to insects, though adders and lizards may sometimes be seen.
Entry to the reserve is beside a road junction just south of Wern Farm, and is marked by small sign. There is space for one vehicle in a layby in front, and more room on a grassy verge opposite. From the entrance, a path climbs a moderately steep, bracken-covered slope then enters a patch of trees and exits the far side via a style, while another path running north to south intersects about half way. The marsh and the sandstone outcrop are towards the south side, near a patch of yew trees, and the old walls are within woodland to the west. All the land in the reserve was originally rough pasture, until the 19th century when the Wern Plantation (pine) was established, though these trees are long since removed, and have gradually been replaced by other species including yew and silver birch.