Nameless Seer Location - Sunken City

My nameless seer spawned in the boss room in the Sunken City map in a location I cannot get to. It looks like it would be on the platform that you could get to during the campaign. It might be because of the ritual was also in the boss room and the final mobs I needed to kill were also apart of that.

https://imgur.com/a/SUuB67r