My next stop was to revisit the Demon Ruins and thanks to the Lord Vessel I could just warp straight to the timid drider girl to save on travel time. After a much easier combat against the demon I fought the last time as well as defeating Kirk the invader, I found an easy and very visible shortcut to a bonfire guarded only by one immobile Rock Worm. At this point I noticed Gravelord signs nearby and figured I'd try interact with one. Oops, PvP time.
The game doesn't really give a lot of info for things like this.
It brought me to the world of another player (a gravelord) whose duty it is to "infect" other players with bad things (which I never actually saw). Another person was already here fighting the gravelord though, and slew him before I could even get close. Still, this banished whatever bad stuff was happening in my world so I was free to continue deeper into the fire themed place.
I soon came upon the Firesage Demon which took a few goes to survive his immolation, but beyond him was a shortcut elevator back to the drider girl's fire which was awesome. Just want to say I really like the level design in this game. Not only are there lots of looping shortcuts to unlock, you can also "see" zones long before you reach them which really adds to the whole world immersion.
A lower corridor then led to a lake of lava (the one I was walking above earlier) to fight a gigantic lava centipede (who I could also see earlier). Fortunately my buddy Solaire is present to tank the beast for me which leads to an easy victory! The ring of lava walking it drops is surely going to come in handy.
It almost killed Solaire too.