Leviathan of Parsonstown is the unofficial name of the Rosse six-foot telescope.
This is a historic reflecting telescope of 72 in (1.8 m) aperture.
It was the largest telescope in the world from 1845 until the construction of the 100 in (2.5 m) Hooker Telescope in 1917.
This telescope was built by William Parsons, 3rd Earl of Rosse on his estate, Birr Castle, at Parsonstown - now Birr in County Offaly, Ireland.
It was recently refurbished is open to the public and is well worth visiting.
Reference: Wikipedia