Go to mahogany town then to route 44 into the ice to Blackthorn City. It worked for me.
You have to go through Diglett's Cave.
blackthorn
You have to navigate through the ice cave
Its right behind blackthorn city
Yes.
After mahogony town befor blackthorn
blackthorn city
in the dark cave near blackthorn city
To Blackthorn City.
Blackthorn city, (east of mahogany town).
you just go south of blackthorn city
Blackthorn City, next to the Pokemart