In order to get to Blackthorn city you must first go through the ice path. My first time doing it it was a real pain in the neck. You need to get a pokemon that knows strength and rock smash. You should get through the first couple of mazes with ease but then you will get to a stage with rocks and ladders. You need to use strength on the boulders and push them in the holes. For a video walkthrough go to YouTube.com and search ''How to get through the ice path in pokemon Heart Gold/Soul Silver. Hope I helped
Ok you must get the boulders in the holes in a path there. You will also obtain HM waterfall there but you can't use it until you beat claire.
To get past the ice cave you need to be smart to be able to pass all the ice skating ice things. It can be really hard, but to get past you need to get waterfall ( got to beat claire stinks I know) its ok then after you will have to put boulders in the holes. Once you get past if you have the rainbow feather go back to professor elm and he will show you on the map where ho oh is ( this is secrect not many people know) after this get to the elite four and you beat the johto next its on to kanto wahoooo
Push the boulders all through the holes using strength
Push all the boulders in the holes.And then slide to the middle.And go down the ladder.
Its a bit hard but you have to go on the ice and try to get to the top. You will also find the HM:waterfall. Hope this helps
Okay, to get past the Ice Cave, you have to go through the cave. DUH!!!!!