If you're able to handle densely packed elite packs there is a dungeon inside the Ruins of Rakhat Keep in the Hawezar region called Iron Hold.
The first part of the dungeon requires you to get the key from the jailer and has a fair amount of ghosts / wraiths. Avoid most of these when possible and just rush to get the jailer.
Head up north to the door and unlock it and go through the challenge room as quickly as possible.
The second section is where you'll find the elite packs. There are typically 2 groups (sometimes 3) of elites packed tightly into the area. On occasion you'll find a treasure goblin as well. The Butcher also seems to spawn with some frequency so keep that in mind.
Use the NM reset to keep the downtime to a minimum.
Typically should take between 2-6 minutes to complete depending on build and class.