Celebrated as one of the world’s most beautiful libraries, King João’s Library, or Biblioteca Joanina, in Coimbra, Portugal, boasts stunning Baroque architecture and a priceless collection of rare books. Recommended by American travel guru Rick Steves, it’s a must-visit destination for bibliophiles and history enthusiasts exploring the University of Coimbra.

The university’s highlight is King João’s Library (Biblioteca Joanina,) one of Europe’s best surviving Baroque libraries, displaying 40,000 books in 18th-century splendor. The zealous doorkeeper locks the door at every opportunity to keep the humidity out of this 300-year-old temple of thought. (Book ahead, as this popular sight often sells out.)

The interior is all wood. Even the “marble” on the arches is painted wood, since real marble would add to the humidity. The resident bats—who live in the building, but not the library itself—are well cared for and appreciated. They eat insects, providing a chemical-free way of protecting the books, and alert the guard to changing weather with their “eee-eee” cry.