Buy Birr Castle vouchers for deals on Entry to Birr Castle Gardens. The staff at Birr Castle Gardens welcome guests to explore its diverse attractions. Once a hub of scientific discovery, the castle now has Irelands Historic Science Centre with various astronomical instruments on display to help educate and inspire today’s generation. Fans of botany can enjoy the landscaped gardens, formal gardens, terraces and water features dotted throughout the grounds; the gardens having been originally constructed around the castle’s lake in the 18th century. In the early 1840s, the Third Earl of Rosse constructed what was the largest telescope in the world at the time, with which he discovered the spiral nature of several galaxies and much more. Visitors can marvel at the restored telescope, which still works today.