Beneath the tarmac of Market Square in Naas lies what may be the last physical trace of a medieval civic building that once sat at the commercial and administrative centre of the town. The structure in question was the Tholsel, a term used in Irish and English towns for a building that combined the functions of a toll-collection point, a courthouse, and a place of civic assembly. Naas had one, and for a period in the seventeenth century it was evidently a well-used public space.

References to the Tholsel of Naas appear in the historical record between 1664 and 1681, after which it was apparently replaced by a new Sessions House. It occupied the northern end of South Main Street, in the old market place, and its layout was quite specific: assembly rooms on the main floor, cellars sunk beneath, garrets above, and an external flight of steps on the southern side providing access to the upper rooms. This kind of arrangement, with public functions stacked vertically and street-level access to the cellars, was typical of such buildings in Irish market towns. By 1997, the Tholsel itself had long since vanished from the streetscape, but during archaeological monitoring of pipe-trench excavations in Market Square that year, workers uncovered the western face of a substantial lime-mortared stone wall, buried between roughly thirty and fifty centimetres below the road surface. The wall, between 1.38 and 1.8 metres wide, was built from a mixture of thin flat stones, pebbles, and small pieces of slate. A short return wall projected eastward at a right angle, and the backfill on that side, a mix of mortar, stones, and sandy soil, suggested these were the remains of the building's cellars. The pipe trench was rerouted specifically to leave the fabric undisturbed.

The walls are now preserved in situ under the square, invisible to anyone walking above them. Market Square itself still functions as the commercial heart of Naas, its surface giving no indication that a seventeenth-century civic building lies just below.