Haven't been idle on the Estate, either; though I don't really mention it much anymore.
I recently redid the arboretum a bit -- setting it up so that when it "rains" every night (the irrigation system runs), it also plays rain sounds. Now, I could have slapped one big ambient on the cell with a fuckhueg radius; but that would be boring. Instead I took two different rain loops of different intensities, set them up to adjust their sound level up or down by ten percent at random, and put out a dozen plus sound emitters all around the cell; so that it will sound different both from day to day, and depending on where you stand in the room. Still fine tuning the exact attenuation so that it's loud enough to be distinct but not overpowering.
And then, I went and did this:
Since I couldn't get an exterior cell to work right; I laid in panels textured to look like the night sky, and scripted them to enable at sunset, and revert to the normal copper roof at sunrise.
The idea worked out so well that I'm going to end up doing two more sets -- one of a blue sky for the day, and one overcast for when it "rains" every night.
So set up, it should look like the center of the ceiling is open at any given time. I figure something like that would help keep people from going insane during long-terms of being stuck in the Estate. It is a survival bunker, after all. Combined with the proper ventilation, sun lamps, and a little air freshening and dehumidifying, it would probably go a long way towards tricking your subconscious into thinking you had access to the outdoors.