That's odd, I still see it. You're not missing out on much, it's essentially a vertical Hylotl airlock.
Didn't expect this to show up ever again.

Hmm, Image Was Removed By @Woa The Author

Yep, but mine has two outside doors and I inside door in the floor.

i see, kinda like the ocean planets under the sea that have the drain system so it doesnt get flooded(on the cities)

Basically it opens and closes the doors to ensure that water NEVER enters the bottom section and drains water from the room when the door are shut.

uh what is that supposed to do? :3