I - Rules
(see JITD, p. 17)
Staircases allow instant movement from one part of the board to another. By using one movement point, a hero (but not a large monster) may move from a space containing a staircase to any space containing another staircase of the same color.
A hero may move via staircase even if the other end of the staircase has not yet been revealed. In this case, the new area is immediately revealed by the overlord player (see Exploring). If the new area is not yet connected to the rest of the map, simply keep the two parts of the map separate until an area is revealed that joins them (assuming one exists).
Attacks may be made through a staircase just as if the two staircase spaces were adjacent. A figure standing on one end of a staircase has line of sight to the other end of the staircase and its adjacent spaces, while a figure standing adjacent to one end of a staircase has line of sight to the other end of the staircase.