Chaos Tower

Chaos Tower is a Unique Zone.
Chaos Towers can appear in any map and have increased chances to appear the higher the difficulty, the chance of encountering a Chaos Tower also goes up, for every map cleared.
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A Quest can be found in the lobby, the chest increases in rewards for each tower you clear, 9 full clears grants access to King Rakhul.

The Quest is exclusive to every Hell difficulty, meaning that Chaos Tower completion only increments on the difficulty in which you have picked up the quest.
Remember to go back to turn the quest in after killing King Rakhul.