The light dims quickly on the way down the stairs. The bright, airy thing the upstairs had going on is quickly replaced by dark wood, tall arches and strong columns, and barely any light whatsoever. What light down make it down to the floor is yellowed, and dust motes float in the beams of light. The books were tall on the first floor, but down here, they positively tower over you.
The walkways between the shelves feel more like tunnels than anything else, and while you can see alright in the dark, you grab a lantern off one of the tables and flick it on nonetheless. You wonder when the last time anyone was down here was.