Cathedral Church of St John the Evangelist

A cathedral of cruciform plan with central tower, built in brown-pink sandstone with slate roofs. The church comprises a five-bay nave with aisles, transepts, chancel, the Harvard Chapel extending along three bays on the north side of the chancel, and further chapels off the south transept. A north porch provides additional entry.

The crenellated tower has a southwest stair turret and two-light louvred bell windows. The five-bay nave features corbelled parapets and four two-light Decorated Style clerestorey windows on the north elevation; the north aisle contains three three-light windows with Y-tracery, and a dormer to St Keynes Chapel with a three-light window. A smaller window lies to the right of the porch.

The north porch has paired lancets to the upper room and three statue recesses, with square-headed windows to the sides and a simple Gothic doorway. The west front displays a five-light window with geometrical tracery, angle buttresses, and a southwest turret.

The north transept has a stepped clasping buttress to the west and a stepped buttress to the east, with three lancets and a small doorway. The three-bay Harvard Chapel contains a central three-light window similar to the nave, flanked by two-light windows with Y-tracery, and has buttresses; beyond the chapel, the end bay of the chancel with a triple lancet featuring a very tall central light is visible.

The east end has five lancets with stepped buttresses and 19th-century pinnacles. The south side reveals a four-bay aisle, allowing sight of a three-bay southwest nave window with cusped circles between intersecting tracery. Aisle windows match those on the north. A long north-south Canonry range is attached to the west bay of the aisle. The clerestorey features three-light windows with intersecting tracery. Three lancets light the south transept end. St Lawrence's Chapel occupies the southeast angle, with an organ chamber above topped by a steeply pitched slate roof.

The chancel displays early Gothic style quadripartite rib vaulting designed by Scott, five lancets in the east wall, and an early 20th-century reredos by Caroe (1937). Groups of lancets to the sides are deeply set and flanked by clusters of slim shafts. To the south stand triple sedilia and a piscina; to the north lies a worn late medieval relief. Elaborate arches to either side open to the side chapels. The Harvard Chapel to the north has a fine southeast doorway with ball-flower work, foliage-cresting to the hood, and flanking pinnacles; it contains a 14th-century tomb of Walter and Christine Aubrey. South of the chancel, the sacristy (rebuilt in the 19th century) has three east lancets and a double piscina. The early 20th-century St Lawrence's Chapel features a re-used 13th-century east window and 20th-century vaulting and elaborate doorways matching those of the Harvard Chapel.

The crossing is defined by four 13th-century arches; the piers to the west arch retain wall paintings of an eagle and an ermine-lined mantle. The stalls were made by Scott. The area west of the crossing was the site of the "Golden Rood", with stairs and upper-level doorways to north and south. The north transept has two early 13th-century arches to the Harvard Chapel. The south transept is similar.

The nave arcade rests on octagonal columns. The roof was restored by Scott but is essentially of the 16th or 17th century; the roof of the north aisle is possibly medieval. In the east end of the north aisle, the former guild Chapel of the Corvizors is now dedicated to St Keyne and is enclosed by wooden screens. The screen to the south is a relocated late medieval example; that to the west is a copy by Robert Thompson, his characteristic mouse signature appearing on an upright. The chapel contains a fine mid-14th-century tomb recess with ball-flower work and effigy, with an inserted contemporary dormer window above.

The cathedral contains stained glass by Clayton and Bell in the south lancets of the chancel, and by Horace Wilkinson in the Harvard Chapel. Fine funerary monuments span the 16th to 20th centuries. In the north transept are those of Reverend Thomas Watkins (died 1829), George Price Watkins (died 1843), and Sophia Watkins (died 1851), the last by I E Thomas. The south transept contains monuments to William Morgan James and Reverend Thomas James (died 1798 and 1812 respectively) by Flaxman; to Walter Jeffreys (died 1748) by Thomas Paty, and John Price (died 1719) by the same artist. Also in the south transept is the bronze effigy of Bishop Edward Bevan (died 1934) by W Goscombe John. Near the Chapel of St Keyne stands a mid-16th-century wooden female effigy from the Games tomb. The north aisle contains an early 17th-century stone monument with alabaster effigies of Sir David Williams and his wife of Gwernyfed, Felindre.

The Romanesque font, dating to circa 1130–50, is stylistically linked to the Hereford school of sculptors. It features a large bowl with a Latin inscription on its rim and reliefs depicting fantastic birds and beasts. The polygonal wooden pulpit reuses parts of a 15th-century screen.