Arrow up walks back through what you have already typed.
How the place is dealt
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01
A setting, then a building
The day's number picks one of six places — a drowned cloister, a signal station on the ice, a glassworks, a seed vault inside a mountain, a custom house on a tideway, a paper mill — and everything else comes out of that choice: the chambers, what the floor is made of, what you can hear, what light there is, and what has been left lying about.
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02
Grown onto a grid
Eight to eleven chambers are added one at a time, each one hung off a chamber that is already there, in a direction that is still free. That is why every exit is a true compass direction and why the map can be drawn at all. One or two extra passages are then punched through where two chambers happen to be neighbours, which is where the loops come from.
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03
Locked so that it can always be opened
Every passage is tested by removing it and seeing whether the building falls into two halves. The ones that do are the only passages worth locking. Locks are then placed one at a time, always on the edge of what you can currently reach, and each key is hidden in the part you can already get to — so the gating is strictly progressive, and there is no way to deal a warren whose key is behind its own door.
The errand goes in the deepest region, behind the last lock, and you have not finished until you are standing back where you came in with it on you. There is no timer and nothing in here wants to hurt you; the only thing you can lose is the thread. Everything you can type is also a button, because a parser is a lovely thing and an obstacle course for anybody who is not already fluent in one. When you are done, the Gambit will play you at a game it invented this morning, the Exchange turns the same number into a market with nobody minding it, and the Almanac files a dispatch from a town that only lasts the day.