Caer Drewyn is the most southerly hillfort in the Clwydian Range and Dee Valley Area of Outstanding Natural Beauty. It is situated on the spur of a hill between Llangollen and Corwen, just above the confluence of the River Dee and the River Alwen. The earliest structure was a small enclosure built against a natural rock outcrop. Today this structure is only visible as the remains of a grass-covered bank. A later, larger fortress was surrounded by a dry-stone wall, and does not have the earthen ramparts of other local hillforts. The area of the site is about three hectares. There are two in-turned entrances, one at the highest point, with the possible remains of a guardhouse beside it, and the other on the west side adjoining the remains of a rectangular building. There is a further enclosure outside that contains stone foundations of what may have been a hut platform.