Forelhost. You can loot hundreds of ancient nord arrows. And that the majority of the enemies there are ghosts. AND that each ghost has a special dagger called a dragon preist dagger. AND if you completed the companions, you can loot the armor of the ghosts. AND there is a dragon preist.
Actually, there are Two Dragon Priests there if you come to that place at a high level and the majority of enemies are Draugr. You only get ghosts in the first few rooms then there are like over 20 Draugrs in one hallway! I can spend about 30 minutes fighting there.
Best thing is... The Draugrs and Dragon Priests spawn there! (A unnamed Dragon Priest will replace the named one) The ghosts do not, which I ain't surprise.