It has folders marked ‘Grasping the victim’s head’ and now – after a £15m revamp and some help from Albert Einstein and the patron saint of the internet – the extraordinary Warburg Institute is letting passersby in to view its ‘books emanating sorcery’

A mysterious cosmic emblem hangs over the entrance to a building in Bloomsbury, at the heart of London’s university quarter. Depicting concentric circles bound by intertwined arcs, it represents the four elements, seasons and temperaments, as mapped out by Isidore of Seville, a sixth-century bishop and scholar of the ancient world, as well as patron saint of the internet. What lies within is not a masonic lodge, though, or the HQ of the Magic Circle, but the home of one of most important and unusual collections of visual, scientific and occult material in the world. Long off-limits to passersby, the Warburg Institute has now been reborn, after a £14.5m transformation, with a mission to be more public than ever.

“We are essentially devoted to the study of what you would now call memes,” says Bill Sherman, director of the Warburg. To clarify, the institute is not a repository of Lolcats and Doges, but of global cultural history and the role of images in society, with a dazzling collection ranging from 15th-century books on Islamic astronomy, to tomes on comets and divination, not to mention original paintings used for tarot cards (about which a show opens here in January). At least half of the books can’t be found in any other library in the country.