[quote=Irisity]
The boss for level 21 is on level 20, Gilmer's tower is on level 20, and Gilmer's tower in itself has multiple floors. Like the dungeon under the Town of Beginnings had multiple floors going deep down. The boss is in Gilmer's tower, Gilmer's tower is in floor 20. It is just on a specific level Gilmer's tower.
[/quote]

Here's an in depth explanation in case you get confused like everyone else did