Yes, you can walk all the way from the terminal to A to B to C and beyond (per-constructed for future concourses D & E). However, for security and safely reasons you are not permitted to do so. I was fortunate to get a private tour and did so in 1993 before the airport had opened (Feb 28, 1995)--construction had been completed but they were still trying to get the automated baggage to work.

• There are several levels of tunnels and getting to the others is not easy as no elevators or escalators are available to do so. The lowest level is the one that has stimulated all the conspiracy speculation.
• The automated baggage tunnel has been long since converted for use by baggage trams.