Dundrum Castle Dundrum Castle is a castle , situated above the town of Dundrum , County Down , Northern Ireland . It was constructed by John de Courcy , sometime near the beginning of the 13th century , following his invasion of Ulster . The castle , built to control access into Lecale from the west and south , stands on the top of a rocky hill commanding fine views south over Dundrum Bay and the Mourne Mountains , the lands west towards Slieve Croob and the plains of Lecale to the east . The Castle is a State Care Historic Monument in the townland of Dundrum , in Down District Council area , at grid ref : J4047 3700 . Origins and ownership . De Courcy ' s original castle may have had defences of earth and timber , but it is probable that the stone curtain wall of the upper ward was built at the beginning of the 13th century . As with other early enclosure walls , there were no towers , but defence was assisted by covered walks along the outside wall - head . An early timber hall may have been sited near the keep , where there is a double - latrine in the curtain wall . In 1203 de Courcy was expelled from Ulster by Hugh de Lacy . The earliest reference to the castle occurs in the mid 13th century " Chronicle of Mann " , which records of de Courcy ' s unsuccessful attempt to siege " the castle of Rath " in 1205 , with the aid of one hundred ships of his brother - in - law , Ragnvald Godredsson , King of the Isles . The castle was then captured by King John in 1210 . Hugh de Lacy strengthened the castle with a massive round keep , probably employing master masons from the Welsh Marches , where such keeps were then popular . Although much of the second floor of this keep was rebuilt in the 15th century , it is clear from the survival of the old fireplace flue and spiral stair that it originally stood at least three storeys high . The basement was used for storage and had a cistern below the first floor , which appears to have been the great chamber for the lord ' s day - to - day living , while the floor above would have housed his private chamber . The castle remained Crown property until de Lacy was allowed to return to his Earldom in 1226 . It was probably after de Lacy ' s second tenure as Earl of Ulster ( 1227 – 43 ) that the twin - towered gatehouse , similar to the one at Pembroke Castle , was inserted in the curtain wall . It has a lopsided design with only one projecting tower to protect the approach along a narrow ramp from the south - west . The stone curtain wall of the outer bailey is likely to have been built by the Magennis family of Mourne , who seized Dundrum in the late 15th century . The Earl of Kildare briefly captured the castle in 1517 as did Lord Deputy Grey in 1538 . During this period it was referred to as Magennis Castle . Phelim Magennis later surrendered the castle to Lord Mountjoy in 1601 . It was made over to Lord Cromwell in 1605 and sold to Sir Francis Blundell in 1636 . The Magennis family recaptured Dundrum in 1642 , but later lost it to the Parliamentarians , who dismantled the castle in 1652 after they withdrew their garrison . After 1660 the Blundell s returned and built a gabled L - shaped mansion in the south - west corner of the outer bailey . This dwelling was ruined by the time the property passed to the second Marquess of Downshire in the early 19th century , though the trees on the hill were probably planted at this time . The castle and grounds were placed in State Care by the seventh Marquess in 1954 . The castle is an important example of Norman architecture , and is a regular destination for tourists and school children . It was the subject of a Time Team programme broadcast on 24 February 2013 . Dundrum Castle , Co . Tipperary . An unrelated structure called Dundrum Castle existed near Dundrum , County Tipperary and was the family seat of the O ' Dwyer ' s of Kilnamanagh , members of the Gaelic aristocracy . Following the invasion of Ireland by Oliver Cromwell and the ill - fated retributive capture of the Rock of Cashel by the last clan chief Philip O ' Dwyer , the O ' Dwyers lost their properties per the Act of Settlement 1662 . Dundrum Castle was destroyed sometime afterwards . In 1730 a mansion known as Dundrum House was built on the site . Dundrum House served as the home of Cornelius Maude , Viscount Hawarden and his descendants until the early 20th century when the structure was sold to an order of Roman Catholic nuns . Transferred to private owners in 1978 , Dundrum House now serves as a luxury hotel and golf club .