Castlemartin House and Estate, Historic estate in Kilcullen, Ireland

Castlemartin House is a restored 18th-century mansion of more than 50 rooms, 27 of them main rooms, with a total area of 2,428 sq. metres. It stands close to the River Liffey at the end of a lime avenue whose trees join to form an arch. A vault of the earlier fortified dwelling is believed to survive in its basement.

Castlemartin succeeded a line of dwellings that may reach back to the 13th century, and a vault of the earlier fortified house is believed to survive beneath the present building. The Eustace family held the estate for centuries; Rowland FitzEustace, 1st Baron Portlester, lived here in the 15th century. The Carter family were later occupants, and the house was restored in its 18th-century form before John Malone bought the estate in 2015.

St Mary's Church, founded around 1200 as a dependency of Kilcullen Church, was rebuilt around 1490 and restored by Tony O'Reilly in 1979–1980 under Percy Le Clerc, then reconsecrated in 1981. Two of O'Reilly's children married there and his mother's funeral was held in it. It is not open to the public.

There is no general access to the estate lands, and neither the house nor St. Mary's Church can be seen from public roads. Entrances off the Newbridge Road are gated and monitored by cameras. The nearest public viewpoint toward the house is said to be along the River Liffey.

The grounds feature an ornate gate from the 18th century and an ice storage building with finely crafted stone detailing at its entrance. These structures reveal specialized preservation and craftsmanship methods from that era.