Hidden cave with tough boss location?

[Willpower]

I ran into that one cave with the circular path that leads into the pit with the really tough enemy hero, and when I entered the cave it said something like "you sense something much more powerful than yourself here". It almost killed me so I left, ended up clearing out the whole right side of the map (no dlc or dynamite cleared areas though) and killed the warden and stuff. Which district or area is that cave located in so I can go clear it?

[Ryvucz]

It's a random spawned cave in Wightmire I believe. The location changes to one of three(?) locations.

[Nishven]

He isn't that tough, if you have nice bleed resist or a way to kit him.

[Saber is bestest]

It's one of the randomly generated elements in the game. Go to http://the-maphack.com/index.php?page=2&lang=en#1 and it will spawn at one of the places labeled Smuggler's Basin

[Myagony]

Port to Burrwich and travel south from there. 3 spawn points. Gutworm is the boss you speak of.

[Willpower]

Thanks everybody, so far I've been playing blind and haven't died yet and its been pretty fun, only other thing I've looked up is how to save and got that figured out.

[Astasia]

That boss is meant to be a much higher level than you and represents a real challenge at that point in the game. Doing a little bit of leveling wont help, it will scale. On some builds it's not worth attempting at all, on others it's super easy.

[PocketYoda]

Just outside of burrwich you'll know the cave you get a "something much higher than you is in here" or something similar..