These are not quests per se: there's no quest objective and no quest giver. The locations appear on your map and you have to go there to see what you can find. The locations are easy to find, though, so it's not like you have to blunder around all over the map to start them.
The first one is Adal Matar, the lost Stronghold, which is an Orc Longhouse veeery high up the mountains to the north-east of Shor's Stone. There's an Imperial camp there, and just above there is a hidden Thalmor camp! The Thalmor try to gain access to the supposed riches in the Orc stronghold, but they can't get past the old Nord ruin that's set in the mountain-side.
So there's actually a lot going on, with a lot of opposition and interesting loot. The Orc stronghold is nice, but contains only two characters. One of them is (apparently) marriagable, and their journals seem to imply that I did marry them -- even though I only walked in for the first time. That's kinda odd...
But the dungeons (both the old ruin and the mine) make up for it! Even though there's no quest objective, they're fun to explore.
This is a screenshot of me enjoying the sunrise up on the mountain side:
The second one is The Frontier to Cyrodiil. Apparently the Thalmor have a traitor in their midst, and this guy will try to escape to the south, to Cyrodiil. The Thalmor closed off the border, having contained the traitor in an old tower built on top of an old Nord ruin -- but they can't get to him because of the beasties in the grove just below the tower.
This one really drives home what ruthless bastards the Thalmor really are: civilian casualties mean nothing to them. But the traitor is not one hair better, so I really enjoyed putting arrows through their throats. The ruin below the tower might be used as a player home, but as long as I can't take my family there, there's no real point.
Again, the story 'emerges' from letters and journals, but there's no real quest objective. But then again, slaughtering Thalmor is its own reward!
Here's a view of a quiet little corner of the ruin. Most rooms in the ruin make great use of (coloured) lighting: