What remains of Templenahoe is essentially the nave of a nave-and-chancel church, the chancel itself largely gone, though stump sections of its north and south walls still cling to the crossing wall and the ghost of a steeply pitched roof survives in the gable line. Dating to around 1170 to 1180, the building was modest in plan, just eleven metres long by six and a half wide, yet the quality of decorative stonework packed into that compact shell is remarkable.

The masonry is a mixture of uncoursed limestone and sandstone, but the builders reserved dressed red sandstone for the details that would be seen and touched. The corner quoins, for instance, are marked by three-quarter columns whose cushion-form capitals carry scallop patterns, bosses, and carved heads. An eaves-course, the projecting horizontal band that runs along the tops of the side walls, is decorated in the same vocabulary. The east wall rises to about eight metres and contains a large chancel arch, originally of three orders though now reduced to two; the inner arch is worked with chevron moulding, a zigzag pattern common to Romanesque decoration across Ireland and Britain, alongside nail-head ornament and foliage on the imposts. On the south wall, a narrow round-arched window cut from red sandstone is splayed widely on the inside to draw in light, and its borders carry a frieze of floral and foliage carving separated by whorls. The west gable, standing close to nine and a half metres, preserves a round-arched doorway of two orders whose hood moulding is studded with conical bosses; the stops at each end were carved as animal heads, though only the southern one has survived. That single surviving head, worn and stubborn, says something about the ambition of whoever commissioned this building and the attrition that eight and a half centuries will do to even well-cut stone.