Low flying rectangle gliding east to west and glowing blue

The object was in the southern sky and slowly gliding east to west. At first I thought it was a banner flying behind a plane, but then realized there was nothing ahead of the object pulling it. This also would have been strange since we were in an area with no real cities for miles, and it was nighttime. It was rectangular and very long, very close to the ground and glowing blue. It looked as if there were tiny glowing rooms inside it, like it was an apartment complex or cruise ship, but these were laid out in intricate patterns.
After we watched it for a few seconds it looked like it slid into a hole in the sky, gradually disappearing completely.