Build a minehole near the beach, walk in direction of water in the mine hole. There should be a wall as in you cant go futher because you have to go down because you are at ocean shallow water. Build mine hole. Keep digging until you hit next wall which is ocean. then you go down like 3-5 mine holes. Keep digging towards the next continenet. Then when you hit DEEEEEEEEEEEEEEEEP ocean, you gotta go down like another 5 mine holes. You cordinate with ppl on other side and now you got tunnels under the ocean.
Maybe people can dig up fossils and shit down there idk