At roughly ten metres high and seven metres wide, it is considerably more substantial than the modest rural kilns one typically encounters, and it has retained enough of its structure to make the original industrial logic of the thing legible, which is rarer than it sounds.

A lime kiln is essentially a furnace for converting limestone into quicklime, a process that required sustained, intense heat from below while limestone was loaded in from the top. The design of the Trantstown kiln reflects that logic carefully. The west-facing front contains an arched recess, just over two metres high and three metres wide, where the stoking hole, through which fuel was fed to maintain the fire, is still evident. Sloping slabs at the rear of the recess would have directed heat upward, while arched niches on either side may have served as sheltered working spaces or fuel stores. The funnel at the top, through which limestone was loaded, is stone-lined, and a ramp to the east gave workers a way to bring material up to the charging platform without having to scale the structure directly. The north and south walls are buttressed to take the outward pressure of the fill, and the top of the kiln is enclosed by a stone wall standing about one and a half metres high, with window openings on three sides and an entrance nearly two and a half metres wide facing east. That enclosure at the summit is a detail not always preserved on surviving kilns, and it gives a clearer sense of how the upper working area was organised and partially sheltered.