Question

I still need to get to the town behind it.

Answer 1

Twist Mountain is inaccessible before you beat the Elite Four. It isn't part of the main story anymore; you need to go to Mistralton City and go on the plane flight to Lentimas Town.

So you can go through it after you beat the main game. Until you do so, Twist Mountain cannot be accessed.

Answer 2

You can go through Twist Mountain after you beat the game. If you are stuck, watch this:
http://www.youtube.com/watch?v=-iwcRFP-Qj8

Answer 3

You go through twist mountain after you defeat the elite four and get the national pokedex. So it is innacessible until you do this. You can get to Iccirus city after through tubline bridge also to get there after you beat the Pokemon league. After mistralton city you go to lentimas town by plane.
Source: experience

Answer 4

Yes you do go through Twist Mountain; it happens after you beat the main story line (i.e. the Elite 4).

You can access Twist Moutain via the Clay Tunnel in Driftviel City.

Marriland's guide on Clay Tunnel

Incidentally, Twist Mountain is where you find Regigigas, but you need Regice Regirock and Registeel to be able to capture him.

Answer 5

There was a cave in at twist mountain before the elite 4 and when you defeat the elite four MARSHAL the person blocking twist mountain will state the mountain is safe to travel through (the company wanted to block icirrus city until the end of the game) so you WILL be able to go there but not until the elite four has been defeated.