When I build my ideal "dream home", I will have a partially sub terranian portion of my house.
Just think, basement larger than the house. At the rear of the house, usually sits the kitchen. Now think that at the kitchen, instead of a wood deck, there is a "garden roof" so you walk right out to the grass, but you are still a good 3' above the ground level with parapet walls all around you.
Underneath the garden roof, in the basement, you have an extra room. Perhaps a play room for children or a home theater.
I've also dabbled with the same idea for a walk out balcony for the master suite. That would be sweet, having a 10' x 10' balcony with grass and flowers connected directly to your bed room. Talk about relaxing!