The map

M opens the full map. N opens a smaller one in the corner that stays out of the way while you play. Both can be open or closed independently of each other.

Where the floor plan comes from

The map is drawn from the game's own tile data - the same data the game consults for its own map - so the shape of the rooms is the real one rather than a guess at where they probably are.

On top of that it adds ground the game leaves off its own map. A board laid across a pit is not part of the room the generator built; it is a prop placed afterwards. The map finds those by asking where things can actually walk, so crossings you can use appear even though the game does not draw them.

The result is a map that is, in places, more complete than the one the game keeps for itself.

What is on it

Height is handled by shading: rooms on your own floor are drawn brightly, and floors above or below you sit dimmer behind them. A multi-level dungeon is a flat drawing either way, so this is a compromise rather than a solution, but it stops the two levels reading as one confusing shape.

Calibration

The dungeon is rotated differently every run and the map works that rotation out on its own, partly by looking at where the lift is. The lift sometimes loads a moment after you arrive, so if the map looks turned the wrong way for a second or two on entering a dungeon, it is about to correct itself.

What it cannot do

It does not show enemies. That is a deliberate line rather than a missing feature.

It does not distinguish a hole from a ledge from a bridge - it knows which ground you can stand on, not what kind of ground it is.

Opening it the instant you arrive in a dungeon may briefly show a simpler map. Generation runs across several frames, and the map waits until the dungeon has stopped changing before it trusts the detailed data.