As the story goes, In 1835 a laborer was digging a trench on a farm when his shovel suddenly disappeared into the earth after thrusting it into the ground. He then sought out local school master Jason Newlove to assist in this discovery.
Here's another design that can be found on the wall. Remember, this was discovered in 1835. Who knows how long it was there beforehand or how they managed to create such elaborate, beautiful tapestries.
The Friends of the Shell Grotto was formed in 2008 to try and help preserve this mysterious wonder for many more decades to come...and to possibly be a part of the rapture when whichever aliens designed this place come back to Earth.