The sign on the tower's front door: reach the top before descending, and no teleporting or phasing inside.
The only information given about The Tower Maze before entry is a simple note posted on its front door: "Warning: If you enter the tower maze, you must proceed to the top before you'll be allowed to go back down. No teleporting or phase allowed in the tower."
Nothing else — no hint whether the tower is required or optional, which is exactly what drove crawlers on The Eighth Floor to debate the risk and conclude someone had to test it. The no-phase, no-teleport clause is what makes the eventual crushing descent lethal: even Everly's hires had no escape hatch once the ceilings started down.
A plain posted note on the tower's front door bearing two lines of text.
The tower's entry rules, and the trap's fine print.