Garnddyrys Ironworks was working c1817-61. The retaining wall, which is probably an original feature of the works, is on the W side of the works, and was necessary because a flat site had to be created on a steep hillside.

The retaining wall is visible for a length of 25m and is partly obscrued by slag, breeze and coal dust that has been tipped over it. The wall incorporates an opening (not original) to a stone-vaulted chamber. The original access to this chamber was not apparent.
R Hayman, Hayman & Horton, 8/1/2004