So, if you exit the introduction with Ralof you'll learn Ulfric was captured up by Darkwater Crossing. I've always known that...but I never actually took the time to look around Darkwater Crossing, thus resulting in this topic.

Specifically - HOW?

Darkwater Crossing is a shack and mine bordered by Salt Marshes on one side...and Mountain Passes in the other.

How was Ulfric ambushed in this area? If he was following the roads, there's no way to encircle a party so there's no place to retreat. The Salt Marshes are extremely easy to evade someone, and there's not enough tree cover to hide a substantial force. So where was Ulfric nabbed? Did the Imperials come spilling out of the mine?

perhaps they set up Camp and the Legion had taken care of any scouts before they were able to report back, making it so the Legion Litterally marched right in while the SCs were unaware because their scouts were slain?

there are multiple times of ambushes

Maybe they were waiting in the mine for him? Ralof did say it was like they (the Imperials) knew they where coming.

Great ,now next time I log on I'm going to look at that area

When I look at the stories regarding the capture, I get the impression Darkwater Crossing used to be a Rift area with a road to Cyrodiil and was later relocated as they changed some details of the map and they forgot to change the relevant dialogue. Given the direction the carriages come from when the game starts, this seems a reasonable scenario.

Could be as there are I think one or two npc's that the Darkwater residents talk about that are not in the game.

I always assumed that the Empire had broken the code that the Thalmar use to contact their agent Ulfric. Then they set up a fake meeting with Ulfric's handler and grabbed him. That would explain why Ulfric did not have many troops with him as he could not trust most of the Stormcloaks to understand his working with the Thalmar.

The Thalmar were also at helgen to facilitate an escape for Ulfric but did not have to after Alduin broke up the whole execution party.

Ulfric wasn't in contact with any Thalmor, that's a fallacy. Ulfric had been manipulated by the Thalmor in the past, yes and escaped their custody thinking he had betrayed the defenses of the Imperial City to the Thalmor (When in truth the city had been taken weeks prior). He was considered an asset to the Thalmor due to that leverage - but the dossier flat out remarks that he is not to be "activated" unless absolutely necessary, since he's a hostile asset.

But you are right in that the Thalmor were at Helgen to negotiate for Ulfric's release. It would give them one more pin to push into Ulfric and continue to fracture both Skyrim and the Empire as a whole, which suited the Thalmor's designs.

All I'm saying is the game establishes Darkwater Crossing as the sight where the Imperials capture Ulfric. I'm at a loss to explain how they performed that feat, given the natural geography of the region seems ill suited for a ambush, or even large troop movements. One has to wonder what Ulfric was doing there at all, unless he wanted to negotiate a deal with the nominally neutral miners for access to their Corundum mine.

Never knew the thalmor were rooting for the stormcloaks, I mean I know they want a weakened empire but then they would have to fight the stormcloaks for skyrim.

I just assumed there was a spy who informed the legion.