See, this fascinating library isn't quite obvious from the outside. You enter this building, and you'll see an interior courtyard. You explore several staircases and then you find this hidden room in the back. They sell entrance tickets, but it isn't prohibitive. And when you get in, you feel like suddenly you're sent a few centuries back in time.
I was there gazing at the collections, and I couldn't help but be amazed at the preserved documents this library holds. It is something that perhaps nerds would definitely enjoy, like me.
I suppose little things like these are what makes Puebla enjoyable for me. I can simply explore the streets and you find little treasures left and right.