137B Mwrog Street

137B Mwrog Street is part of a two-storey terrace that includes 135 and 137, forming a group. The terrace is built from coursed blocks of squared stone and features slate roofs with brick stacks. The openings are topped with segmental heads made of stone voussoirs, except for the right-hand bay of 137 and 137B, which have cambered stone heads. The windows are wooden casements with either two or three lights. The rear is reportedly made of painted rubble.

137B itself is a one-window cottage that is continuous with 137 on the left. It has a small rendered stack on the right. The entrance is located on the left and features a segmental head with a raised rusticated surround, along with an inset 20th-century panelled door. There is a window to the right of the entrance, with a corresponding window above on the upper storey; both are two-light small-pane wooden casements that have replaced earlier three-light casements.

The interior has not been seen as of December 8, 2005, but it is said to contain a massive beam extending from 137.