It looked like beach rock to me. but I'm not a geologist or marine engineer. Over the years I've spoken with people with pretty good credentials and to be honest most don't buy into Atlantis. There are a few who think that ocean voyagers going back to before the common era could have been in the area and trading with the local indigenous people. They think the wall might have been some kind of harbor or break water when the ocean level was lower. The Phoenicians are a popular choice as culprits, but they run the gambit. You see strange lights in the sky at night, but most are nothing more than harmless drug runners or harmless special operations forces doing their thing. The strange lights in the ocean are nothing more than bio-luminescence creatures that come out at night.
We were doing a night dive once, and the ocean is a much different place after it gets dark. Even if you know there is no such thing as sea monsters, you really can't tell what might be coming at you out of the dark! So there we are in about 30 feet of water, and out of the darkness came the biggest manta ray I had ever seen. It had a wingspan of at least 15 feet from tip to tip. The krill that Mantas feed on were coming out because of our lights and this manta was gorgeous as it flew up with its mouth open and engulfed the krill and it became quite friendly, it almost gave you the notion he knew you were giving him food.
One popular theory is that Bimini was where the fabled Fountain of Youth was located. There is a freshwater spring in a mangrove that pumps out thousands of gallons of water that flow out to the ocean. It was there that people were going to bathe and just after a few minutes they would not only feel better, but were euphoric in both a physical and emotional way. The water was analyzed at the U of Miami back in the 80's and found out it had an abnormal high concentration of.......................LITHIUM!