The Wren Library of Trinity College. Designed in 1676 and completed in 1695 it remains one of Cambridge's most stunningly beautiful edifices - although this picture does it no justice. It's free to get in and its contents are incredible, ranging from my personal bedtime-reading favourite, Newton's Principia Mathematica, to A. A. Milne's autograph copy of Winnie-the-Pooh - which is my actual bedtime reading favourite...