This is just a quick way to try and get extra experience with Mighty Blow and Massacre. Generally 30-40 mobs in the area.
Act 1 - Quest 9 "The Imprisoned Angel"
Talk to Leah to start the quest. Head to the Waypoint for Leoric's Manor. When you get there, go back inside Leoric's Manor. On the way back to Leoric's fireplace (great way to find Leoric's Shinbone as well) and round up all the monsters that are barring your way. I used a wizard, so teleport helped me get them in one spot. Diamond armor + meteor = dead. Of course I was doing this in Nightmare at level 53 because I am trying to get all the stuff for the staff. Doesn't matter what level monsters they are, you still get the same experience bonus for Massacre and Mighty Blow. I was getting 3k+ for Mighty Blow and 4k+ for Massacre. Shinbone is rare, so you will be coming back and forth a bit.
529.885 XP before run
544.782 XP after run
I know it isn't much XP. But the level difference I am guessing plays a crucial part in the XP gain. Also there is always a chest inside the manor making Chestmaster 2000 that much closer to achieve. Not saying you will go in there 2000 times, but that is a lot of chests to get and any bit can help.