You need to have done the following before you're able to proceed to the following route, the Ice Path to Blackthorn City.
Here's the list:
1. Go to the Lake of Rage and defeat/capture Red Gyarados.
2. Talk to Lance at the Lake of Rage.
3. Head to the Mahogany store, and you will see a small cutscene leading to a secret stairway to a Team Rocket Hideout.
4. Navigate and clear the Team Rocket hideout.
5. Defeat the Mahogany Town gym leader.
6. Return to Goldenrod City and defeat Team Rocket at the Radio Tower and at Goldenrod Underground.
Have fun! :)
-emma
Here's the list:
1. Go to the Lake of Rage and defeat/capture Red Gyarados.
2. Talk to Lance at the Lake of Rage.
3. Head to the Mahogany store, and you will see a small cutscene leading to a secret stairway to a Team Rocket Hideout.
4. Navigate and clear the Team Rocket hideout.
5. Defeat the Mahogany Town gym leader.
6. Return to Goldenrod City and defeat Team Rocket at the Radio Tower and at Goldenrod Underground.
Have fun! :)
-emma
