Not necessarily in order of significance, the following are American Destinations undiminished over time according to Gecko

#1 Colorado River canyon at Glenwood Springs, Colorado
#2 West Coast beaches of the Big Island of Hawaii
#3 Mammoth Cave National Park, central Kentucky
#4 Snow skiing at Steamboat Springs, Colorado
#5 Fisherman's Wharf, San Francisco, California
#6 Wild trout fishing on the Newhalen River at Lake Iliamna, Iliamna, Alaska
#7 Specific to The Maid of the Mist, Niagara Falls, NY
#8 Authentic Mexican food, Alamosa, Colorado
#9 Gettysburg National Military Park and Cemetery, Pennsylvania

Can you add Number Ten?