The architecture at Stapleton is a mixed bag, with much of it having a throwaway character. But not the FBI Field Office that opened last summer: It was built to last. The building, which was privately developed and is being leased to the FBI, was designed by Chicago's Skidmore Owings and Merrill, which also did the Air Force Academy as well as many oil boom-era skyscrapers in the city. Though made almost entirely of reflective glass, the Field Office is very secure — as might be expected, given its function — because believe it or not, those big window-walls are bomb-proof. But the building is also quite chic-looking, something that can only rarely be said about the G-Men and G-Women working inside.