The first-visit description

A room can carry a first time block: prose shown in place of the standing description the first time the player sees the room, after which the ordinary description takes over.

create the Maze Heart
  a room

  first time
    You did not expect the hedge maze to open out like this: a perfect
    circle of turf, silent, with a single stone chair at its center.

  A circle of turf enclosed by high hedge walls. A stone chair faces
  the way in.

This form is rooms-only and first-time-only: second time and the other ordinals are load errors here. (Inside behavior bodies, the full ordinal family is available; that different construct is covered in the flow chapter.)