The Clandeboye Estate is a country estate located in Bangor, County Down, Northern Ireland, 12 miles (19 km) outside Belfast. Covering 2,000 acres (8.1 km2), it contains woodlands, formal and walled gardens, lawns, a lake, and 250 hectares (620 acres) of farmland. The estate is currently home to Lindy, Marchioness of Dufferin and Ava, widow of the last Marquess (the title being extinct).
Clandeboye was first settled in 1674, but the Clandeboye House of today dates from 1801, utilising a design by Robert Woodgate that incorporated elements of the previous building and was built for the politician Sir James Blackwood, 2nd Baron Dufferin and Clandeboye.
In memory of his mother, Helen, Lady Dufferin (granddaughter of the playwright Richard Brinsley Sheridan), Lord Dufferin and Ava built the stone edifice Helen's Tower on the estate, which has since been immortalised by Tennyson in the poem of the same name. The tower has taken on an unforeseen poignancy, as an almost exact replica of it, the Ulster Tower, was built at Thiepval to honour the men of the 36th (Ulster) Division who fell at the Battle of the Somme. The estate was used for army training during the First World War, and the 36th (Ulster) Division trained beside Helen's Tower before leaving for France. The tower can be reached via the Ulster Way, a five-mile (8 km) section of which traverses the estate.