ATLANTIS FOUND (By Me) In The Sahara by The Puzzler | [Archive link just in case]

Because everyone is acting like Bright Insight is the originator (even though he himself said he learnt about it from a documentary), but this poster came up with the theory independently in 2008, and appears to have had everyone tell her she's wrong. I don't know enough about geology or geography to know if the theory is plausible, but it's still fun to speculate, and give The Puzzler the credit she deserves.

PS I believe it's pronounced Ree-shaat not Rickart.