Mountains... deep thoughts...

Well... do you actually need 6-8 movement to pass a mountain square? Because at 1 movement turn/unit going through a mountain wouldn't slow a unit down all that much compared to the plains. Unless you make passing a mountain a multi-turn affair, in which case they're practically impossible to move over anyway except by very fast units.

I'd rather not have units able to traverse over mountains, not only for the gameplay impact also for scenario reasons, where the scenario designer might want to block off certain areas from players.

well i would prefer mountains to be impassable as well, unless a mountainwalk spell was cast on the unit or something. 

Why not add quests that reveal hidden paths through so called impassable mountains?

I like the idea of finding tunnel networks, and hidden passes.

Also Make mountains like asteroids in GCII. At first though you can't traverse them. Later on though maybe with better training, equipment and or what not its possible to traverse mountains. In the later game units can travel over them a little faster. It just takes a few turns to get over them (early on like 6-8 turns but later on like 3-5). So depending on how long the mountain range is if you want to hike it or not.

Though some are impassable because its so dangerous. I think you feel safe in the beginning of the game and later on those natural defenses well don't work like they use to.

What do you guys think?

or a skill called mountaineering for letting units guide others through the mountains?

But still at a high moment cost, I mean they're mountains after all and getting a unit of siege engines through em is a bit of a challenge.

Ya different units will have easy times getting across, (mounts of horses and bears) and yes siege units will take longer time getting over (engineers: "god damn it my back") with all that heavy equipment...

Isn't there a spell that lowers mountains? Who needs to walk over them when you can just make them vanish.

Mark me down for mountains being at least nearly impassable.  How many dark age peasants with a set of armor and a spear could hike their way through a real mountain range?  

I could live with some sort of mechanic (spell, "guide" npc skill, something) to ocassionally mitigate it, but in a world bereft of food, technology, and basic human survival items (especially early game) I can't see people putting together the provisions to go on a serious mount trek.  

I'm perfectly happy with the occasional pass between mountain ranges like the on guarded by a monster lair in the northern portion of the current beta map.  

I like the idea of "Most" mountains allowing travel over 4-5 turns. (a multi turn affair) ... then SOME mountains are impassable.

So for instance, mountains take 4 turns per 10 soldiers to pass through, while Alpine Mountains are impassable.

Then, when you attain "snow gear" or "snow climbing" ... or some such, then mountains take 2 turns per 10 soldiers and Alpine Mountains take 4 turns per 10 soldiers.

This.

How about, instead, of an attrition system when passing mountains ? Just like Hannibal crossing the Alps

I like the idea of mountains being somehow passable.
Give them varying degrees of dangerousness and difficulty so that you can have impassable mountains where they are needed for a scenario, while allowing passage for other mountain ranges, only that you have to fear your army getting worn down (like gapper said). With special gear, abilities and/or spells you then could decrease the difficulty and the danger of passing through this terrain (as Tasunke said).
I never liked that Civilisation-modell of "always impassable" mountains.