Maughan Library, Kings College Uni
Although it looks straight out of Hogwarts, this noble building in the heart of Chancery Lane, aka Legal London, has been the main library of Kings College University since they acquired it in 2001. Known as the Maughan Library after a past graduate and major benefactor to the Uni, it was originally built to house the newly formed Public Record Office (PRO).
Prior to 1851, government and court records were kept in in various locations and conditions around London. In fact one of the principal locations was in St John's Chapel incorporated within the central White Tower at the Tower or London which also contained the entire country's supply of gunpowder, the tower itself lit by candles on account of the rather small windows and lack of natural light. Anyone see a potential problem there?
Given its purpose and the risk from fire, the interior of this new building consisted of many box-like storerooms that had to be self-contained with strong iron doors and lit externally, which is the reason for the large number of wonderful expansive windows. However the building soon outgrew its original requirements and there were several phases of further building work with stone being quarried from different locations and this clearly shows on the facade in places (see pictures)
Fans of the Da Vinci Code may know the Library when it was used one of the locations consulted by Robert Langdon and Sophie Neveu in chapters 92 and 95 of the Dan Brown novel and although those rumours still persist that the round reading room was used as a filming location for Dumbledore's Office in the Harry Potter films, sadly that isn't the case.
There are tons of other Harry Potter locations used around London that you can see though, so hit me up and we can take a flying tour. Disclaimer - you'll need to have your own broomstick.