Before you start a run, head to the Options menu and click on the dwarf located near the screen's lower right side. A "Secret Dwarf" prompt will appear, and you can replace that text with Skip #, where '#' is anything from 0 to 36 and represents the floor to which you wish to skip. Note that you can only do this before you begin a run. You'll head directly from the tavern to the desired level, and return to the tavern when you're done.