You will gain an optional objective to pick the Snow Onions if you head to the West and into Obliteration Station. There you will find numerous Marauders coming after you. Head deeper in (or to the West to the Garden of Murder and you will be facing more Blaster Nomads. Furtyher on you start to find Cannibal Rats you need to deal with.
Once in there you will encounter more Horned Skags. They are followed by some Nomads and Maniacs then more Horned Skags and 2 Badass Marauders. Head on over to the South and then start up the stairs you find there.
At the top of the stairs you have even more foes to deal with. There are more Marauders for you to kill plus a few Maniacs and a Blaster Nomad. Just deal with them then press onto the West on this rampart to move on forward. This leads to the final area: The Colosseum of Laceration.
After him is Assassin Rouf. This Rat-type enemy will be running around and attacking with his shotgun. It helps to keep him as a distance as much as possible (or just charge in there) to cut the damage from him. He is very fast so keep on the move.
The final foe is Assassin Oney. This is the hardest of the 4 Assassins as he will rush you and in general be a nuisance.
Defeat the assassins and, if you are level 72, it will unlock the Overpowered Enemy feature.