John Constantine has taken up residence here. Around the door and windows sigils are carved to alert him if someone is in. Stairs leading upwards to where he sleeps and works (the head librarian's old office) have a few wards that will either turn a person around or paralyze them for a short time. Nothing is deadly but meant to stop a walker if they managed to get in or keep a living person away from what spellcasting stuff he's scraped together.