The Laurentian Library in Florence is a depository of rare books and manuscripts begun by Pope Clement VII (a member of the Medici family) and was meant to both showcase, show off, and propagandize the Medici family name, and to hold their 10,000+ rare manuscripts.
It features architecture and, more specifically, a famous staircase that was designed by Michelangelo.That's the main draw. He was old... like, REALLY old, and kept apologizing that he couldn't remember what the staircase was meant to look like, while it was being constructed.
They held off completing it, waiting for his design, and eventually he sent them something; but it likely wasn't what he'd originally conceived of (decades earlier) and either way - it was completed after his death. The library is considered a masterwork of his Mannerist style.