File:The Old Library, Queen's University - Geograph.org.uk - 1208102.jpg
It was constructed 1865-68 to a design by Lanyon, Lynn and Lanyon with later additions (1911-14) by Lynn and (1951) by John MacGeagh. While it looks very much like a converted chapel, the building has always been a library; inside it has been sadly altered by modern restructuring.
Queen's has many different libraries spread throughout the campus - this is now part of the Main Library. See also 717216.