SPOILER
No it's not the door to the right where you fight Kangaxx, the twisted rune encounter is in the Bridge District.
It's the first right facing door on the waters edge of the map from the Bottom of the screen.
And it's a bllody hard fight
Incidently Waverider will you please put spoiler in your posts because you've given away one of the pivotal plot twists in your last one. Thanks
(Not that it bothers me but it might annoy those who haven't finished the game yet.)