So to do this, first dig under ground at least 8 blocks. place the command block, and activate the command. I f you do not want bedrock, that is customizable.Also, If You want a special way to get in, use these commands:/give @p sign 1 0 {BlockEntityTag:{Text1:"{\"text\":\"Junk\",\"color\":\"white\",\"clickEvent\":{\"action\":\"run_command\",\"value\":\"tp @p <X> <Y> <Z>\"}}"},display:{Name:"Custom Sign"}} and /give @p sign 1 0 {BlockEntityTag:{Text1:"{\"text\":\"Leave Base\",\"color\":\"dark_red\",\"clickEvent\":{\"action\":\"run_command\",\"value\":\"tp @p <X> <Y> <Z>\"}}"},display:{Name:"Custom Sign"}}. To use these, place the sign "Junk on a chest full of, well, junk, and the other sign in the base. using F3, swap the <x> <Y> <Z> area with where ypou want to teleport.