This article is about the castle in Birr, the town in Ireland. For alternative meanings see: Birr (disambiguation).Birr Castle (Irish: Caisleán Bhiorra) is a large castle in the town of Birr in County Offaly, Ireland. It is the home of the seventh Earl of Rosse, and as such the residential areas of the castle are not open to the public, though the grounds and gardens of the demesne are publicly accessible. The „Great Telescope“ and other features See also: Leviathan of Parsonstown A main feature on the grounds of the castle is the „Great Telescope“ or Leviathan (aka The Rosse Telescope) of the third Earl of Rosse, an astronomical telescope with a 183-cm (72 in) reflector. It was completed in 1845 and was used for several decades before the last observations were made in the first years of the 20th century. Its record size was not surpassed until the completion of the 254-cm (100-in) Hooker Telescope in 1917. It was dismantled in 1914, but was restored in the 1990s and is open to the public. Laurence Parsons, 4th Earl of Rosse and his mother were eminent photographers and her darkroom, which is also on show, is believed to be the oldest surviving example in the world. The grounds of the castle contain the oldest wrought-iron bridge in Ireland, dating from 1820. The walled gardens in the grounds feature Box Hedges that are over 300 years old. They are also, according to The Guinness Book of Records, the tallest hedge in the world.