Tread-wheel, Castle Place, Omagh, Co Tyrone, BT79 5ER

A detached single-cell double-height stone tread-wheel house, built around 1800 and located within the former Omagh Gaol complex at Castle Place. The building is rectangular on plan, facing west, with a hipped natural slate roof fitted with angled blue and black ridge and hip tiles.

The walling is constructed of random rubble basalt built to courses. Windows are square-headed painted timber six-light casements with dressed sandstone surrounds and sills. The principal west elevation is asymmetrical: the left portion is uncoursed rubble with a red brick eaves corbel, whilst the right side is sandstone ashlar over a splayed plinth with a sandstone eaves corbel. The upper storey has two windows positioned at either end; the right-hand window sits above a square-headed entrance opening with a painted timber half-door. Above this entrance, a painted sign reads "TREAD WHEEL." The doorway has dressed sandstone jambs and lintel.

The north elevation is inaccessible. The rear east elevation contains four openings at upper storey level; the right-hand upper storey window is infilled with concrete blocks and surmounts a square-headed replacement door clad with corrugated tin sheeting. The south elevation is rendered, revealing coursed squared and tooled sandstone walling at the rendered reveals, and features two square-headed double painted timber vertically sheeted doors.

The tread-wheel is sited in the centre of the former gaol complex, situated west of Castle Place on an elevated site visible from Abbey Street to the south. It stands northeast of the former gaol gatehouse and east of the former Governor's House. The wider gaol complex, begun in the 1790s and opened in 1804, also retains the Governor's House (built 1823) and various remaining structures now used as housing to the south and east. The original prison cells, arranged on a half-octagonal plan, have been entirely demolished except for surviving four-metre-high boundary wall features to the west.

Historical records indicate the tread-wheel was of small dimensions and its power was applied solely to raise water for the building from a deep well adjacent to it. The tread-wheel was an important structure in the management of prisoners. The gaol complex closed in 1904. The building is shown on the First Edition Ordnance Survey map of 1833, and by 1905–6 the gaol site was recorded as disused. The structure is a rare survivor of this particular building type. The building is recorded as currently derelict and is located within a conservation area.