The Wall of Holes...
The inscrutable, featureless grid is a daunting puzzle that stands between you and the goal, escape, or gaining an element for the next step in the quest....
Can close observation, probing, or clues provided elsewhere lend information toward the solution? Or will some other luck or insight be of assistance in solving this conundrum?
Possible solutions for the discerning DM:
Put spikes or similar into the correct holes:
Primes, Fibonacci sequence, multiples...
Perhaps clued elsewhere in the dungeon - a sigil, religions sign, symbol of a significant NPC.
|Something like this....|
A single, correct hole with coordinates:
"Was it 5 up, and 7 across, or 7 up, and 5 across? I can't remember...."
Treat it as a combination lock, with a particular sequence to trigger:
Consequences of failure?
Well, you're stuck in that flooding room.
Something has snapped off a probing finger.
A trap is triggered by an incorrect sequence.
Maybe it resets after a period of time - but does the oxygen, food, light hold out for as long???
Or maybe they're just filled with those little blowgun darts...