Birr Castle is home to the Irish Historical Science Center. It is an interactive museum dedicated to early photography, engineering and astronomy. Particular emphasis is placed on the world-famous Grand Telescope. Here you can see, among others photographic equipment used in the 19th century and electrical and engineering equipment originally owned by Charles Parsons and used in his experiments. Part of the exhibition is devoted to botanical works carried out in Demesne.
The castle is also the seat of the 7th Earl Rosse, but the residential part of the building is not open to the public. The first Anglo-Saxon castle was built here in 1170. The present building, however, was not built until the 17th century.
There is a 300-year-old hedge in the walled garden. According to the Guinness Book of Records, it is the tallest hedge in the world. The castle is also home to Ireland's oldest wrought-iron bridge, dating from 1820.