Use styrofoam for most of the raised structure to reduce weight and stress on the aquarium itself. You can recover part of the lost room by providing pvc pipe tunnels into the raised bank.
Either way it looks like it would be a very natural looking set up when complete.
sorry, thought that was funny.......... but it looks like a good idea, i would use just one large U shaped pvc and lay it on its side, then pile the sand/substrate on top of it. or use multiple smaller ones for multiple "homes for the fish....................... aquatic fairies....stilll funny
I had a setup like that a while ago. I buried a "goldfish bowl" on it's side in the gravel to make a cave. I had 2 problems (minor ones).
1. If I didn't syphon it VERY well, a lot of stuff would collect in all that gravel.
2. I would completelt bury the bowl after every water change. By the next water change (next week), the hill would have slid down and the bowl would be half out. Here is a pic. Oh, and FYI, this was my wife's tank. All the sissy fish. Well, she calls them "the happy fish".