I know this will be hard to answer and some people will just ignore this..

By walking through it, xD.

Ok, to be serious:

Upon entering, go north, up the stairs and go across the bridge, into one of those ladders, to B1F. Push the boulders out of the way and use Rock Smash on the single rock, not the two sitting next to boulders. Walk past there and go up the stairs and go across the bridge. Down the stairs, battle a trainer, and then find the ladder to B2F. Battle the trainer and surf. Go up the Waterfall, battle the last Winstrate guy, grab the item, then go left and go down the waterfall. You'll come across another ladder. Enter it to come back to B1F. Push the boulders in the right pattern and enter the next ladder. Go up the ladder, across the bridge, down the next ladder, then you'll be at the end.

Glad to be of help.

Hard? Yeah...you go up the water and go all the way around and find a stair..go there and find your way out...There will be strong opents before you can get out..so watch out..

The easiest way is to have some Pokemon (they do not have to be your main party, just some sucky ones) know Flash, RockSmash, Strength, Surf, and Waterfall. First, use Flash to see better. Then, when you come across one room that has water in it use Surf, and Waterfall. The easiest way to see where Im talking about is if you come across a CoolTrainer named Victor. There are two waterfalls near him and the first one you see, and the one you have to go up, should be the one to his right. If not then you probably took a wrong turn. If you took the other way, have the Flash on that way you will not have to have battles with people you cannot see. Keep going through and you should see one area that has two boulders and two breakable rocks and they should be in opposite positions or across from each other diagnolly.There is also no little place to put the boulder is placed until you see the ladder. Then the last person you have to fight has a Cacturne and somethig else (Peliper I think). Then you should find the exit. I hope I helped.

Just go down the laders until you get lucky enough to find the exit. I recommened you buy the stratgy guide or search online for a map to make it easier.