That's an altar of storms, as has been said. If I had to wager a guess, it's the altar of storms in blasted lands, specifically.
When blizzard makes outdoor dungeons, they take a copy past of terrain, plop it down onto a blank level, and then design the dungeon on top of that. Because Karazhan takes place in deadwind pass, and because you can see parts of deadwind pass from within Karazhan, they took a chunk of map focusing on deadwind pass and some of the surrounding area and plopped it down. That chunk just happened to include the altar of storms.
If the dungeons DON'T rely on you seeing "outside" of them (like most BC dungeons) they're literally floating hallways above flat blank canvases of land.