How do you get to blackthorn city in souls silver?

Answer 1

First, you have to have already done the following:

1. Gotten the Cianwood Gym Badge.
2. Gotten the Olivine Gym Badge.
3. Beaten Team Rocket in Mahogany Town.
4. Gotten the Mahogany Gym Badge.
5. Beaten Team Rocket in Goldenrod City.

Once you have done all that, the man to the left-most point in Mahogany Town should let you through. If he stops you to buy a RageCandyBar, just buy it. You'll need it later on as the game progresses.

Continue heading left and (after most likely facing a series of Trainers) you should have reached a cave called Ice Path (make sure you have a Pokemon with the move Strength with you and [optional] some Fire types to handle all the Ice type Pokemon in Ice Path). You might want to catch some of the Ice type Pokemon in Ice Path because the gym leader of Blackthorn uses Dragon types, which are weak to Ice.

Once you make your way through Ice Path, you should be in Blackthorn City.

Hope this helps!