Head over to Grahtwood, or travel to a friend to make your way to Craglorn. Once there, head over to the Ruins of Kardala (Marked on the map below!)
Grab some guildies, or post in zone - you’ll have a group in no time at all.
Inside this dungeon, you’ll find ghosts patrolling around stone statues. Attacking these ghosts while they are within proximity of the stone statues will cause the statues to come to life. These statues have a chance of dropping Spirit Shard that can be used to summon a VR11 boss. Killing the boss grants around 37,000 XP, and much loot. The boss can be summoned and killed multiple times per run. Once all the ghosts have been killed, and all the bosses summoned, simply exit the instance and reform your group to reset the instance.
With an efficient group, you’ll generate around 1.5 million XP per hour.
The boss has 38k health, but the fight itself is very easy. I was able to heal for a group of VR2 -6 that didn’t even have a tank, and we had no problem at all.