How do I build a stairwell through multiple levels?
Assuming you're building down:
- Build a down stairway on the first level from the designate (d) menu.
- Build up-down stairways on the levels before the bottom from the designate (d) menu.
- If you have a defined "bottom" level, build an up stairway on that level from the designate (d) menu.
You will need to switch your view's "z-level" to build the levels. You switch "z-levels" by using < to go down a "z-level", and > to go up.
As per the Bay12 dev-log, you will be able to designate over z-levels in Dwarf Fortress version 31.26 and beyond.
Though the accepted answer's method will still work, you will be able to do the following (again, assuming you're building down):
- designate a downward stairway on the top level (or build a stairwell if there's no dirt/stone to carve).
- Start designating an up/down stairway one level below (change z-levels with '<' and '>')
- Go down to the penultimate z-level, and finish designating your up/down stairway.
- designate an upward stairway on the bottom level