The duergar puzzle wall is very distinctively duergar; no other dwarves make anything like it, and no other race makes anything similar in scale—even the gnomes with their well-documented love of trickery.
The puzzle wall can only be found in large permanent duergar settlements (or at least intended to be permanent). The wall serves to separate two spaces in a duergar settlement. Generally it serves to separate the religious heirarchy from the general populace. Both sides usually like the arrangement, as it makes it harder for one side to usurp the other, and usurpation of power is a classic duergar problem.
The puzzle wall is actually two separate “devices.” The puzzle part of the puzzle wall is built of high-quality masonry and (again usually—there are few absolute truths for anything duergar) bristles with magic and psionic energies. The puzzles are text-based (rune-based, really) and are built into the wall as it is built. There is often more than one puzzle involved, and puzzles can and do interact. Failing a puzzle usually activates traps or summons creatures. These traps are usually fatal, and the summoned creatures fight to the death. Successfully solving the puzzles opens a magical door in the wall; the magical protections make it impossible to find this door without solving the puzzles. The other half of the device is a more mundane magical separation. A wall of magical force (or something similar) sits just on one side of the puzzle wall. This wall usually has a key (magical or otherwise) that could be operated only by the king/queen.
No one has ever found an intact puzzle wall that ceased to function because of age or decay. They built these fuckers to last, even if they didn’t. And note that both parts of the wall must be opened to pass through.