You must be referring to BLACK City, as Blackthorn City is exclusive to the Johto region (only found in Pokemon Gold, Silver, Crystal, and Pokemon Heart Gold and Soul Silver).
The amount of people in Black City changes each time you link-up on WiFi.
To get to Blackthorn City, you must defeat (or catch) the red Gyarados and find Team Rocket's hideout in Mahogany Town. Then head east to Ice path. After that youre in Blackthorn City.
Destroy them.Go outside and play sports not Pokemon!
1st : Everybody happy 2nd : simple connection
If you have defeated the Mahogany Gym, you have to go to the Goldenrod Radio Tower and defeat Team Rocket. After that you can go to Blackthorn :)
You can find Fraxure outside Victory Road.
It is just outside of Black City, just exit to the left and follow the road.
i originally asked this question.i think you have to go through dark cave,to the end in black -thorn city although to do that you need to teach a Pokemon flash.that would just make it easier for you to navigate through it.i can't do it because it is too hard.
You can find it in the outside area or relic castle
Not origanally I don't think but if you trad migrate or link Pokemon yes( the link is right outside of black city or white forest
The Irish word for 'blackthorn' is draighean, and a blackthorn stick would be bata draighin.
You can find it outside of Dragonspiral Tower and wait for rippling water.
There's a lady outside in Undella town as you enter from the south. Speak to her.