For reasons beyond my comprehension, nearly every circular door in existence uses hinges. This idea is to put the door on/in a track, and roll it out of the way of the doorway.
Making such a door easy to open and close is a bit tricky, but this *is* the halfbakery.
I say "nearly every," because google found precisely one rolling door, [link], but it's not precisely a widely known to exist architectural feature.-- goldbb, Oct 28 2015 Bank with rolling door. https://www.google....e89b98981b1!6m1!1e1 [goldbb, Oct 28 2015] Old idea! http://biblehub.com/luke/24-2.htmThis Idea may not be original enough. [Vernon, Oct 28 2015] The rolling rock (Even Gollal) https://he.wikipedi...2%D7%95%D7%9C%D7%9C [pashute, Nov 01 2015] bigsleep, you mean that if I posted an idea about an dilating door, it wouldn't get marked as WTCTTISITMWIBNIIWR, or something similar?-- goldbb, Oct 28 2015 For a halfbaked version, the door you seek is used in airlocks on Deep Space 9.-- lurch, Oct 29 2015 too much like a revolving door?-- travbm, Oct 29 2015 Not anything at all like a revolving door, [travbm]. Try reading for comprehension this time.-- lurch, Nov 01 2015 You may look into ultrasonic levetation and magnetic levitation. The circular door has a hole that seals up one way and closes another as it rotates.-- travbm, Nov 01 2015 [pash], for some reason your Wikipedia linked page comes out upside-down and back-to-front on my screen.-- MaxwellBuchanan, Nov 01 2015 Must be the Australian localisation.-- pocmloc, Nov 01 2015 random, halfbakery