Every area should have a distinct purpose - Don't add empty rooms to pad the looks of a map. Keep it economical and keep the rooms stocked. Some prefer the daughter, some prefer her mother. The easiest way to keep one player from dominating the other. Exposure - Force players to expose themselves when some items are needed.
Power has a price.
In the air, you are more exposed and more vulnerable. That should be self-explanatory, nobody wants to play duel in large maps running around on an endless bug hunt. Or if you really need some dark areas to emphasize your architecture, at least light the floor. Audio clues - Always make areas sound differently according to player's interaction. Rote - Make the surroundings interesting and easy to memorize.