The site occupies the crest of a steep-sided ridge running north-east to south-west above the Severn Valley. It enjoys wide views except to the east. The castle stands on a rock platform up to 6m above the bases of the ditches which define its north-east and south-west ends. The north-east ditch, 30m wide and 3m below the natural ground level, has a bank 1.5m high outside it, while that to the south-west is narrower. A drawbridge led from the town across the south-western ditch to a simple gate in the curtain wall. The modern track up passes some slight platforms which may mark the site of buildings in the Welsh town. A temporary entrance ramp has been constructed over the fragmentary northern castle wall to facilitate excavation and consolidation.
The plan of the castle, mostly recovered since 1980, consists of a rectangular curtain wall enclosing, at its western end, a large rectangular keep, and at its eastern end, a round tower. Both these features are integrated into its circuit, the keep by its south wall where the latrine shafts are situated. The main ward lay between the keep and a round tower at the opposite end of the castle, but the keep was set in a small courtyard on to which the main entrance opened. The building seems to have had the usual first floor entrance most keeps have for reasons of security, but with a ground floor door added later. A rock-cut ditch runs across the castle court from north to south.
The excavations showed that repair work had been carried out to the masonry of the keep and it had been divided internally. These may have been the repairs recorded after the castle was captured by the English, since some of the materials used can be traced to sources in English hands. Excavations also indicate that ranges of buildings lay along the southern and northern sides of the courtyard. Stone balls, which may have been fires from English siege engines in 1277, have been found scattered at the site.
The irregularity of plan of the native Welsh Castles has often been commented upon, the terrain in which they were built being an obvious influence. Several of the 13th-century Welsh castles lack the systematic arrangement of carefully planned and distributed mural towers and gatehouses found in English castles of the same date. Dolforwyn falls into this native Welsh tradition, for there is no gatehouse, simply a gate protected by the keep, admittedly an arrangement also found in Norman castles of south Wales. There is also only one certain mural tower. A rectangular keep is also an unusual feature for a late 13th-century castle in Britain. The Welsh castle of Dinas Bran, situated high above Llangollen, and possibly built in the 1260s, is very similar in plan to Dolforwyn. It also has a rectangular keep, although the entrance which it overlooks takes the form of a twin-towered gatehouse.