While searching for a good one to share, I ran across this one on Listverse. They are a great source of so many different topics, it's hard not to borrow from them!
This one will start you to thinking, that's for sure!
The sailing stones are a geological phenomenon found in the Racetrack Playa (a seasonally dry lake located in the northern part of the Panamint Mountains in Death Valley National Park, California, U.S.A.). The stones slowly move across the surface of the playa, leaving a track as they go, without human or animal intervention. They have never been seen or filmed in motion and are not unique to The Racetrack. Similar rock travel patterns have been recorded in several other playas in the region but the number and length of travel grooves on The Racetrack are notable. Racetrack stones only move once every two or three years and most tracks last for just three or four years. Stones with rough bottoms leave straight striated tracks while those with smooth bottoms wander. Stones sometimes turn over, exposing another edge to the ground and leaving a different-sized track in the stone’s wake.
Various and sometimes idiosyncratic possible explanations have been put forward over the years that have ranged from the supernatural to the very complex. Most hypotheses favored by interested geologists posit that strong winds when the mud is wet are at least in part responsible. Some stones weigh as much as a human, which some researchers such as geologist George M. Stanley who published a paper on the topic in 1955 feel is too heavy for the area’s wind to move.
Now this is a mystery that all the science loving folks out there can get their teeth into, don't you think?
We can have some fresh coffee out on the patio, but the heat is coming early these days!