Plas Tan-yr-Ogof including adjoining walls and arches to E and W

Rectangular 2-storeyed house of local limestone rubble with limestone dressings and cast-iron Gothic windows. Crenellated and corbelled battlements with flat roof. The main entrance is contained within a storeyed and battlemented porch projection set back and adjoining to the E; three concrete steps up to deeply-chamfered Tudor-arched entrance with recessed modern door. To the L, on the return of the main E wall of the building, is a fine, large Tudor-arched 6-light window, with Perpendicular tracery of cast iron. Two-light Tudor windows to both floors of the main (road-facing) facade, with cusped heads, diagonal iron glazing bars and flat, returned labels. A further, single-light window appears to the centre; this was formerly a segmentally-headed entrance. Above it, between two Tudor windows, is a projecting sandstone shield, its heraldry or inscription lost; to the L a large out-of-character modern entrance with double doors. To the rear are 6 pointed-arched entrances with 6 fine, pointed-arched tracery windows above; modern external fire escape to that to far R, modern window insertion above second from L. The battlemented parapet continues here, though uncorbelled. Further arched window to W side with deeply-recessed intersecting tracery and small-pane glazing; ruinous mono-pitch lean-to below with semi-ruinous 1m high rubble walls adjoining to N. Adjoining to the E and running parallel with the road, a short section of rubble wall stepped-up at a Tudor-arched entrance. Beyond there is a further 60m of crenellated wall, some 1.5m in height, the crenellations widely-spaced; this terminates at its junction with a further stretch of lower rubble wall with 'cock and hen' coping.

Adjoining the porch to the W and running along the roadside is a 3m high stretch of corbelled and crenellated wall. In the centre the wall steps up above a wide Tudor-arched entrance; beyond it continues as before to adjoin Tan-yr-Ogof Farmhouse.

The interior was not inspected at the time of survey (5/97).