Atlantis-This will take mabye like 2 minecraft weeks
Get a bunch of building material you hate using like dirt or cobblestone. Easy part. Find a nice piece of water. I dont care how deep or wide you want it. Slowly, make the material like you make a house on a new world. Then, close it up with all material. mine a hole in it. get inside your house, make a door, and add one wherever. Hard Part. Make a lot of picaxes and shovels. Then take out your wall.and build a little 3 block tall pathway with roof. Then put your wall back into your house. slowly expand your pathway so you will be able to build freely inside a big old underwater dome. Then get whatever material you like... Build houses and a palace for yourself. Make a wall around your city (i recommend cobblestone), with like a double door or something, and boom. You got your own Atlantis.