Cilgerran Castle (Welsh: Castell Cilgerran) is a 13th-century ruined castle located in Cilgerran, Pembrokeshire, Wales, near Cardigan. The first castle on the site was thought to be built by Gerald of Windsor around 1110–1115, and it changed hands several times over the following century between English and Welsh forces. In the hands of William Marshal, 2nd Earl of Pembroke, the construction of the stone castle began after 1223. After passing through successive families, it was left to ruin and eventually abandoned by 1400. The castle backs onto a cliff face, with the remaining ruins dating from the 13th century. It was most heavily fortified where it faces inland, and includes a pair of drum towers rather than a central keep which remain. It passed into the hands of the National Trust in 1938, who open it to the public.
The castle sits on a rocky promontory above the River Teifi, with one side directly onto a cliff face. An earth and timber castle is believed to have existed prior to the current building, but was destroyed by Welsh forces. The existing masonry dates from around 13th century. The walls facing the cliff top were the least heavily fortified, with the defences concentrated on those that faced inland. These comprised two lines of defence, with an outer bailey and two drum towers rather than a central keep as typically seen in other castles of this period. The gatehouse is located in the south east of the building, and only partly remains. A ditch around the outside of the castle was cut from the rock face, which is thought to have once been spanned by a pivoting bridge. Cilgerran Castle is the most northerly of all castles in Pembrokeshire. It is twinned with Cardigan Castle, located on the opposite bank of the river 3 miles (4.8 km) downstream.