While on vacation, I traveled through the Atlanta airport, a major Delta hub, and I found the architecture very internesting. Specifically the atrium and the subway system. I am thinking about making an airport in Hammer, or at least a building with similar architecture or the subway. Similar to the transit system in Half-Life, except at much higher speeds and in small tunnels. Maybe the normal walkway collapsed and you have to get into the transit tunnels via a vent or maintenance door. Ever play Decent 3? If you have, you may remember the high speed train system. Maybe something like that.