stairs at the front of a Noh stage
Refers to the steps that lead from the stage over the white gravel (白洲) separating the audience from the stage in a Noh theater. A highly domain-specific architectural term.
See also: 白州
On a Noh stage, performers enter by climbing the stairs at the front of the stage.
白洲 is the white gravel area itself, while 白洲梯子 specifically refers to the stairs that cross it.
Compound of 白洲 (しらす, 'white gravel area') and 梯子 (はしご, 'ladder/stairs'), describing the stairs that cross the white gravel in a Noh theater.