I hadn't heard of this -- I visited the websites and managed to find the dates of some future "events":

quoted text BUNKER TOURS quoted text Bunker Tours are generally offered daily to registered hotel guests as well as the general public. Tours > > quoted text are approximately 90 minutes in length and are available for guests 10 years of age and older. quoted text quoted text At the conclusion of the Bunker Tour, participants receive vouchers good for $5 off The History of The > quoted text Greenbrier (book) or The Greenbrier, America’s Resort, The Brief History (DVD) available in The > quoted text Greenbrier Shoppe & Newsstand. quoted text quoted text HOURS (subject to change) quoted text 9:30am - 3:30pm, Daily quoted text
quoted text RESERVATIONS quoted text General Tours: 844-223-3173 quoted text Groups (15+) & Private Tours: 304-536-7810 quoted text quoted text No tours are offered: quoted text April 3 - 6, 2017 quoted text October 30 - November 2, 2017 quoted text December 25 quoted text - See more at: http://www.greenbrier.com/Activities/Bunker-Tours#sthash.ebleXUtY.dpuf You're welcome guys and gals