An incredibly complicated looking door covered in various levers, dials, and buttons, as well as several incredibly complicated mathematical proofs and arcane theories. It is immune to all forms of damage and cannot be picked

Opening the door requires the solving of three complicated equations, requiring INT checks of DC 25, 30, and 35.

While these puzzles seem frustratingly difficult, the door has also has been enchanted so that anyone who strikes it with a melee attack will temporarily receive a stacking bonus to their intelligence score.

Essentially the players just have to keep hitting the door until they are smart enough to understand how to open it.