The Secret Behind Gracen's Home, The "ancient Century"

So today I did the quest "Lost in the Jungle" and when I finished the quest one of the rewards was access to Gracen's home. So I decided to take a look and I found a block with coordinates scribed on it. The coordinates where "-701, 15, -275". I decided to take a look and I went towards the coordinates. What I found was a temple ish thing with nothing really in the temple. But by random coincidence I right clicked on a pedal thingy for the block meanwhile I held the block so the block was placed. Then a door opened up and a boss was in the room. As a lvl 63 Assasin it wasn't easy to kill but when I killed the boss I got nothing and it just respawned. I was confused and decided to search the name of the boss "Ancient Century" but nothing came up on the forums nor the wiki. Now I am even more confused and I am posting this to know if anyone knows about this or if you know what purpose the room has.

Thanks!

 

It's a grind spot

 

Oh, I am so dumb. Well thanks for the info!