Connection points to Mistralton Cave and Twist Mountain
The connection points to Mistralton Cave and Twist Mountain are accessed after heading to the west side of the first room (after the entrance) until you see some Workers standing by a bunch of boulders. You have to talk to a Worker in a group (in the center of the group). He will ask if you have a Pokémon with Rock Smash in your party. (If you do, great! If not, go get one yourself. If you don't have the TM, get it at Virbank Complex.) If you have a Pokémon with Rock Smash in your party, the boulders will be removed. After entering the room blocked by the boulders (after doing the whole talking to the worker thing, obviously), go to the western part of the room you're in (doesn't matter if you surf in the water, take the land route, or whatever, just get there) and you will notice two doors. One (the smaller one) leads to Mistralton Cave. The other (the big one) leads into another room. From here, go all the way north until you see ANOTHER big door. Go in here, and you'll be in the Ice Rock room of Twist Mountain - take the entrance from here out into Regigigas' room or go out of the Ice Rock room into the bigger Twist Mountain area.
You may ask, "Why did you waste all my time with this long direction cheat sheet?!" Well, I said it because I feel that it needs to be noted on the actual article - obviously, in better formatting. (while you're at it, remove the Strength boulder text from the trivia section - if it has a non-decorative purpose, e.g. being able to be cleared to lead to another area - it's not trivia!)