The well predates the building entirely: before anyone drew medicinal conclusions from its waters, it was apparently venerated as a holy well, though historical sources disagree on whether it was dedicated to St Patrick or St Peter. That ambiguity alone says something about the layered and slightly contradictory history of the place.

Mallow Spa had become a fashionable resort by the 1720s, drawing visitors who believed the mineral waters offered therapeutic benefit. The Spa House itself was built in 1828, designed by the architect George Pain in a neo-Tudor style, complete with half-timbered gables, latticed windows, decorative barge boards, and numerous individual chimney stacks. Writing in 1837, the topographer Samuel Lewis described it as containing a pump-room, a room for medical consultation, a reading-room, and baths supplying salt-water, vapour, and medicated treatments. By the 1840s, however, the spa had already begun to decline, and several attempts to revive it later in the nineteenth century came to nothing. The building survives in modified form, its ornate Victorian character partially softened by later renovation; the stonework has been exposed and the original windows replaced, leaving it rather plainer than Pain's original design. In 1857, before the final decline had fully set in, Sir Denhem Jephson Norreys extended the spa's reach by piping its water to a purpose-built public watering place on the west side of Spa Walk. That structure, known locally as the Dogs Heads, is a sunken rectangular enclosure lined with ashlar limestone, approached by steps from the street. Along its west wall runs a trough fed by water issuing from the mouths of three carved stone lion heads, with cast iron hand pumps on a platform behind. It is an oddly formal piece of civic infrastructure for what was, essentially, a horse trough with social pretensions, and it is the most intact survival of what was once a small but earnest attempt to make a North Cork market town into a place of fashionable cure.