So Yesterday I was looking for the Lover's Stone (although I was apparently slightly in the wrong area) when I stumbled upon something very weird. I was bunny hopping up this mountain pretty much due east of Markarth. Coming from Salvius Farm it's past the first bridge and mountain, you should come to a crossroads with a roadsign. When you look down from the ledge into the water you can see a boat crashed on the shore of the mountain and there is a Flawless Diamond in it. On the world map it's the large island in the middle of the river east of Markarth. There doesn't appear to be any discernable path leading to the top of the mountain, so I had to jump to get to the top (I just went there again and using Shadowmere or another horse is way easier) when i got to the top I found something very strange. There is what appears to be a temple of some sort, although it doesn't show up on the compass. I say appears to be, because I can't get to it. It's surrounded by an invisible wall all the way around it. I was wondering if anyone knew what this place is all about? It's altogether very strange, and I wouldn't be suprised if it's some future DLC locale.

It's just across from Kolskeggr Mine? If so, fret not! You'll get there during the main quest.

Yeah it is. You can actually see it from the ledge so that makes a bit of sense. Weird that they'd surround it with a wall ala New Vegas though. Telling me I can't go somewhere like that just makes me want to go there more.

That temple has a strange similarity with cloudruler temple in Oblivion. That was what I though the first time I got there, before doing the MQ

Indeed, it's significant, but the proper way to it lies elsewhere.

Don't seek out the way inside. You'll (possibly) break the main quest