Past a rope bridge in the Catacombs (which I accidentally break and kill myself on *sigh*), I find a strange and ominous chalice. Because the door past it doesn't open I decide to poke it, which teleports me into a really dark landscape occupied by a massive giant skeleton who breathes poison and summons his regular sized minions to battle too. Alas for him, his bling stands out so much that it is clearly evident what his weak spots are. A few broken bracelets later and he explodes (from shame I guess), which opens the path to the picturesque city of Irithyll.
Gee, I wonder what I should attack?
I opt to go back to that rope bridge though, since breaking it seems to open the path down to a huge and almost empty lake. The giant crabs on one side are easy to avoid, and so is the giant electric purple worm. The giant ballista that keeps shooting at me, not so much! At least I can get it to kill the worm for me. While looking for a way up to it to shut it down I find a small cave with Horace waiting inside - he's gone evil so I am forced to kill him.
Where's Anri, you bastard...
I also find the Old Demon King, who for a change, has a belly weakspot. This actually makes it tough to get at him, and I fail a few of times. Fortunately there's a bonfire nearby and when I ember up I also find assistance in the form of Knightslayer Tsorig (I guess getting rolled over by the skeletons muddled him up) as well as Cuculus of the Great Swamp, a pyromancer student of Corynx. While both are slain in battle, they weaken the Old Demon enough for me to finish it off. I could have probably left the lake at this point, but I really wanted to shut down that ballista.