Colossal Cave, Vail, Arizona - Tours are given daily, on the hour, year-round. You need no special clothing in the Cave, which is always 70 degrees and dry and you are welcome to take pictures inside. (Photo via Instagram by @gotmet)
It broke my heart when the Bamiyan Buddhas were destroyed... without ever discussing them before, my little Harry has started asking when he can see the remains. I hope Afghanistan is stable enough one day.