It was built, according to Mark Bence-Jones, by the 5th Earl of Inchiquin in honour of the actress Sarah Siddons, the most celebrated theatrical figure of late eighteenth-century Britain and Ireland. The tower appears on the 1842 Ordnance Survey map simply as "Bathing Ho.", which tells you something about the distance between a building's romantic origins and its eventual practical use. It stands roughly five metres in diameter, has a fireplace inside, a crenellated parapet, and a door facing east. The lower courses, slightly wider and built with a base batter, the outward slope at the foot of a wall that adds stability, may be older than the rest.

The house that gave this estate its purpose was a large early-to-mid eighteenth-century structure, possibly incorporating an earlier castle on the site. Its front ran to six bays between two three-sided bow windows, with prominent string courses and quoins, and a Gothic chapel wing was added in the nineteenth century. The armorial slab of William O'Brien, who lived from 1694 to 1777, was salvaged from the house and is now held in Cork Public Museum. Three cut limestone milestones, dated 1734, survive on the wall of a causeway to the south of the site. The house itself was demolished in 1944, leaving the estate's outlying features to accumulate their own quiet history. A free-standing Doric column, the kind of solitary ornamental pillar that Georgian estates occasionally scattered across their grounds as eye-catchers or commemorative markers, was recorded on the 1934 Ordnance Survey map under the name "Pedestal". A walled garden, now overtaken by trees, and a crenellated waterfront wall with the remains of a terrace that carries a faint resemblance to a battery also survive.

What remains at Rostellan is less a ruin than a dispersal: fragments of a substantial estate scattered across the shoreline and its surrounds, each one carrying a slightly different layer of the same story. The Siddons Tower is the most legible of these, its seaward windows and interior fireplace suggesting something more considered than a simple bathing house, whatever the map may say.