Up/down stairway

From Dwarf Fortress Wiki

This will carve an up/down stair into a wall, which acts like both an upward stairway and a downward stairway on the same tile. Unlike a downward stairway, this cannot be designated on a floor. If no wall is present it can be built using the build interface (bCx).

Carving up/down stairs

1. Press d to open the designate menu.
2. Press i to select "Up/Down Stairway".
3. Move the cursor to a position on or near a wall and hit Enter.
4. The spot you marked blinks + indicating where the area you wish to start carving stairs.
5. Move the cursor to any position across the area you wish to carve up/down stairs and then press Enter again. This area must be a non-built wall. Any area of floor or construction will not be selected. Usually, this is just a single tile.
6. The wall tiles in the area you defined should blink similar to mining.
7. Wait for a dwarf to do the job. You will need to designate/build a down stair on the z-level above and an up stair on the z-level below for each up/down stairway, or you can just use more up/down stairs.