Easy "What are you rubbing at anyway?" Achievement
This rune can be found in the Old Sewers, you need to kill special elite, very big fella. There could be others elite around the level so if you want to be sure that you are close to the right elite, there will be some dude behind bars with wich you can talk. Also you will need to just quite down (place from which I can't climb normaly up). Make sure to be well prepared!