The next floor of the tower looks to have been some kind of indoor arboretum - once. The large chamber is decorated with trees and bushes, but all drip with a sticky black tar. Motes of dust and ash float through the air over empty flower beds, lit dimly by pale light coming from somewhere beyond the trees.
It takes the party a moment to notice that the light comes from outside the tower - the whole back wall of the chamber is actually open to the air, presumably to have allowed natural light into the garden back when it was alive and thriving.
The companions have just a moment to remember that the outside of the tower is just as dangerous as the inside, when they hear something large move between the trees nearby. Ducking back into the stairwell, they see one of the squido-griffs pass between the shadows of the trees, scraping its bloated flank along one tree and making a mess of the tar.
It doesn't seem to have noticed the heroes. But where there is one of these creatures, there will likely be more.
Judging by there being yet another set of stairs leading higher, this level must not be the highest floor of the tower.