1 Mordekai: So we've tried going over the mountains, under the mountains, and teleporting through the mountains. And failed each time.
2 Lambert: There's only one option left. Go around the mountains.
3 Alvissa: The Orcrift Mountains form an impenetrable range 800 miles to the north and to the south!
4 Lambert: Exactly. It'll be much quicker that way.

I originally wrote this as 1800 miles north and south. Which does sound a whole lot more impressive, admit it.

And then I thought... 1800 miles north, plus 1800 miles south, times 1.6... that's nearly 6000 kilometres. Holy cow! That's almost far enough to stretch from the tropics to the polar regions! Okay, that's a bit too far.

Checking it later, I find that it's a bit less than the length of the Andes. Okay, so you could have a mountain range that long, since clearly one exists. But wow, I don't want to delay the fantasy guys that long.

(All this assumes they are on a planet the same size as Earth, but that's pretty much de rigueur for fantasy stories. I guess setting them on something significantly different is stretching something just for the sake of stretching it, and not particularly conducive to story elements.)

(Of course, I could be wrong...)

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2022-12-17 Rerun commentary: When I make a mountain range impenetrable, as Alvissa says, I really make it impenetrable.

It's lucky Kyros is in the background here, because the other option would be to blast the mountains into oblivion.