On 2 April 2017, the YouTube Channel "UFOmania - The truth is out there" published a video about an ancient city that was allegedly discovered beneath Cades Cove, a valley in the Great Smoky Mountains:
This is not an original report from UFOmania. The narrator's script, as well as the photographs, originally appeared in an article published on experiencecadescove.com on 1 April 2017, which was, of course, April Fool's Day. In addition to the highly suspicious publication date, the article ended with the following paragraph (emphasis ours):
For information about seeing the underground city in Cades Cove, don’t check back here. This entire story has been an April Fools’ Day joke! To the best of our knowledge, there aren’t any subterranean cities located beneath the Smoky Mountains. However, there are plenty of wonderful things to see and do above ground in Cades Cove. To prepare for your next visit to the Smokies, check out our guide to the Top 6 Cades Cove Activities You Don’t Want to Miss.
There were several other clues that this article was an April Fool's Day prank, albeit an elaborate one, and not a genuine news report. For one, the article included an image purportedly showing a tweet from the account @GSMNPNews: