Cut doors and windows (saving the door piece for a hinged door), and make a ladder from 2x4s and dowels.
Note: The safe building, engineering and use of the following project is entirely your responsibility. The description is how I built it and may not be appropriate for your home layout or intended audience. The guidelines for use and parental supervision are identical to what they would be on a backyard or outdoor playground. It is not inherently safer just because it is indoors.http://www.creatrope.com