Do Anyone Know Of A Hidden City Underneath Detlas?

I was using wyntills and optifine on wynncraft the other day and somehow my optifine decided not to load a random chunk in the middle of detlas, through the chuck error I could see alot of underground structures (seems like sewers or a small city). I wondered how can I get there so I went to the wynncraft wiki and in detlas section of the article about easter eggs i found this:

• There is an Anti-Bovemist lair within the city walls.
  • While this was rumoured to be true, no evidence from previous versions of the map have shown that there was any lair.

Do any of you know what is that and how can i get there?

 

The ruins I believe are part of this secret discovery (spoilers) https://wynncraft.gamepedia.com/Ruins_of_Detlas

 

There is a secret discovery as ocel0tgirl said that entails those ruins.