Somewhere in the middle of the game you'll participate in the Arena contest. Once you win that, you'll catch the attention of Lady Grey. She'll invite you to Bowerstone North. After this point, you'll be able to access Bowerstone North freely.
actually people have dug their way through to the other side of bowerston north in the beginning of the game. i don't know how it is done but i would like to know how if any one knows some hints, please tell me.