Allt-yr-yn Lock and Little Lock, with intermediate bridge and basin, Monmouthshire and Brecon Canal

Allt-yr-yn Lock and Little Lock, located on the Monmouthshire and Brecon Canal, features lock chambers constructed from both rubble and brick, with tooled sandstone copings. There is a rebate for a removed lock gate on the eastern side. At the western end, a rubble weir is present, with splayed retaining walls extending beyond it. Immediately to the east, there is a narrow bridge with a segmental arch, made of roughly dressed stone voussoirs. The bridge has splayed parapets with tooled chamfered copings, although some of these have been partly replaced with cement. East of the bridge, there is a stone-lined basin that is approximately 12 metres long. The Little Lock chamber also includes a rubble-built weir at the western end and rebates for removed lock gates at the eastern end, with its walls made of rubble and brick and squared sandstone copings. Additionally, there are straight retaining cheek-walls to the east of the Little Lock.