This can be accessed by using the Corrupted Jewel, created from the Pure Light and Pure Darkness. These can be acquired from the Light Portal and Dark Portal.
There will be many Level 45 Tanks along the Corrupted Path, but they do not take notice of the player, being too busy killing each other instead. These are all either called Insane (Tank name) in which case they will be blue as normal, or Corrupted (name), in which they will be scarlet and have cracks. There is a cave at the end of the path. The path will split into three different paths. Follow these other paths.
A boss is at the end of each path. Corrupted Wizard is a Triangle with spawners out of each end, and is red and cracked. It has 400HP and spawns Overlord drones, 4 of them, at a 5 stat point reload rate.
Corrupted Vanguard is a Pentashot. It is red and cracked and had 400HP just like the others. It can also shoot Fireballs occasionally.
Cave and Boss