Thanks, I had found that. But if you start exploring the northern/northeastern overworld (it's an entirely new overworld map), the Blue Ring only helps a little. The "northern overworld" has pretty hard enemies - I could use a red ring or potions.
Once I bought the blue ring and had only 5 rupees, I visited the old man for door repair. He can have my 5 rupees.
I have now finished Level 6 (mostly by cowering in the doorways and firing sword beams into the rooms to kill everything), but I can't find Level 7 yet. By the way, you can get the magic sword with only 10 hearts in this quest. I have also found the master sword, but not enough hearts to get it.
Update: It's really remote in the northern overworld, but there is a shop with a guy that sells potions (without needing the letter). So, the old woman's shop still does nothing for now.
Edited by Gold Ring, 25 March 2016 - 10:52 PM.