greenbrier resort with a >> you want us to do what? >> reporter: he asked them to build a 112,000 square foot underground bunker beneath the hotel, and keep it secret. this was a serious matter that required novel thinking. >> right. it's pretty phenomenal. it's a hell of a story. >> reporter: greenbrier historian bob conte says it was ingenious. there was a ready made cover story, the hotel was expanding. >> somebody comes up with the idea, "we'll build two buildings. we'll build an overt building and a covert building. we'll do it simultaneously." >> when the project began, the lakeside golf course was nine holes. go somewhere. >> where did the dirt come from? the bunker. >> reporter: three years of construction later, there were 18 dorms, a hospital clinic, a giant auditorium with exactly the number of seats for every member of the house of representatives. even a studio for tv broadcasts. this feels kind of scary. >> it is scary. >> reporter: all deadly serious. this is where they came to get cleaned off? these showers designed for the newly arrived congressmen to be fallout. up to 240 people an hour. >> no time for modesty. and the c

. >> reporter: the greenbrier bunker. >> the floor is five feet thick, the walls are five feet thick, the ceiling is five feet thick. we're in a big concrete box. h hotel, this facility was built during the cold war to house congress in case the u.s. capitol was destroyed by a nuclear bomb. these showers were for the congressmen to be decontaminated from nuclear fallout. >> clothing would have gone in. it would have been burned in an incinerator in the power plant. >> reporter: the nuclear fears of the cold war may be a thing of the past but each year a cabinet member is still asked skip the state of the union address. >> they are then put in a secure location with a support staff before the state of the union begins. and they're brought back only the next morning. >> reporter: former u.s. attorney general alberto gonzalez once served as the designated survivor during president bush's 2007 address to a joint session of congress. >> madam speaker, vice president cheney, members of congress, andrews air force base. there were a group of individuals there from various departments and age