I hereby challenge all of you to build a blanket fort of your own. Can you best my engineering brilliance?!? Or, alternatively, just have a ridiculous amount of fun in doing it? (Yes, to that second one!)
Post pics!

Corner 1 held up by a lamp (only plugged in and turned on for the photos, normally I just open a corner to let light in.)

Corner 2, my couch wall was not high enough, so I installed some shelving that also serves to raise the roof.

Corner 3, used a mat that was in the living room for one wall, though it doesn't serve much structural purpose. You can see that I have fit my mattress in here, and it is as comfortable as it is awesome.

Corner 4, a box spring mattress serves as a wall opposite the couch side, and helps hold the main roof blanket up nicely. This part is where the door flap is located.

I plan to expand with a moat and portcullis.