I'd like to see transparent everything. Well, almost everything.
Transparent floors, walls, ceilings, tubes.
Think of large aquariums with the plexi-glass wall built into a tank or the side of lake. Or walking or riding through a tube underwater.
Transparent walls to make a item, such as a restaurant, seem like it's open-air, but the wall keeps out or in stuff you want to keep out or in.
Transparent paths that take on the texture of the ground so it seems like your guests are walking in an open field for that state fair feel.