The underground headquarters of the Agency, located in Boston, on the Cambridge side of the Charles River.

The location is old. Some areas are very recent and high-tech. Other levels and sectors look like they date back to the WWII era, or even significantly older than that. Its origin is a mystery.

There are multiple entrances into the Complex -- side roads into tunnels, warehouses with car lifts, service corridors and roadways from the Big Dig and other means. Indeed, one reason why highway and tunnel construction around Boston has been so difficult has been from potentially interference with elements of the Complex. (How the Agency has finessed around that is not known.)

The location provides easy access to different transportation hubs, particularly airports. You rarely use the same airport more than once in a row.