Here is a little something I've been working on.
...but fueling it all, at the centre, is wealth unimaginable. A regenerating diamond capable of fueling the prison's magic for the duration of eternity. A gem that splinters off tiny fragments of itself every millennium at a rare conjunction when the stars are aligned.
Few know how to reach the prison, and those few who do know the truth are never stupid enough to undertake the journey themselves. Instead, they send adventurers to raid the prison; they rarely expect to see those adventurers alive again.
This dungeon exists on two layers within the one page. Each a different colour, and each revealed by the application of coloured cellophane over the paper.
When characters walk into the prison, they are like the prisoners and are prevented from passing walls of any colour. As soon as they touch a mystic alter, their body phases into alignment with one of the colours. Once this occurs, they take a circle of cellophane matching that colour and overlay the map with themselves at the centre of this circle. The cellophane indicates which walls are still solid to them, and obscures the walls that they may now walk through freely. Once they reach another altar, a character may choose to touch it (thus shifting their phase alignment and colour of cellophane) or continue past.
If the a character comes into contact with one of the imprisoned beings, they cannot be reasoned with...these are psychopathic, world-destroying beings. Survival might be a possibility, but critical injury and lifelong scars will come from every encounter...and a second encounter along the way is likely to be lethal when that confrontation occurs in a weakened state.
This is a dangerous place, and the stakes are high.
I'm just refining the colours now, a one-page dungeon for this place of nightmare should be available shortly.