I was wondering if anyone has actually work it out.

I've been having a walk around the rift and the top of the map.

I am thinking the forts will be in opposite corners the Dawnguard in the bottom right and the vampire fort in the top left.

There are two main islands in the top left which I think could well be used. One is Orphan's Tear wrecked ship which is my first guess. The second is between Solitude Lighthouse and Brinehammer.

In the Rift I noticed a platform in the mountains between Followstone Cave and Tolvald Cave near Riften. When you stand looking at the area it doesn't quite match up but they may add the paths and take a couple of trees out. Otherwise my guess is perhaps behind Riften.

Anyone else been looking to see if they can find the locations and have any good ideas?

I heard it was down that road near Falkreath, the one that goes to Cyrodiil but is "blocked".

Also, the forts won't be in the current map. They said they would open up blocked off parts of the map then you'd be able to go in the area. The Vampire Stronghold is past Solitude, more north than the game allows you to go currently.

Todd said they would be next to a tree near a mountain

The vampire stronghold should be west of Northkeep in an area not accessible as of now.

Dawnguard castle seems to be in an area in or around the Rift, judging from the vegetation seen in the screenshots.

cool. Thats a good thing. I was read on a previous post somewhere that the forts will be be in an area already on the map and then there is a realm off the map..

Happiness all round

+1

that narrows it down, lol