Made some good progress on this last night, ended up playing until about 2am without realising it - so I'm paying for that today!
I killed the Old Demon in the Smouldering Lake, first few goes I tried to take him out too quickly and he had a few really annoying attacks which floored me if I was up close. In the end I went for a mix of cautious sword attacks followed by a retreat and some ranged attacks from my trusty longbow. He didn't stand a chance
Following that I did some more exploring of the Catacombs, found a bunch of pickups and enemies but can't see anything else I'm supposed to do here other than the boss that you fight when touch the goblet? He spanked me pretty hard a couple of times, so I decided to head back to some previous areas as I've had the feeling that I've been following a single "thread" through some spaces which might have more to offer to me... turns out I was right!
So having headed back to the road of sacrifices I found a boss that I completely missed the first time around, Crystal Sage, who proved to be a walk in the park to anything else I'd encountered (presumably as I'm possibly now somewhat overpowered for this area?) and this then lead to a whole new Cathedral area. I spent a very merry time here working my way through hordes of zombies and other creatures, before finishing up by taking out some giant in a big central chamber. It was a this point that I realised it had ceased to be Sunday night and was now Monday morning, so I thought I would call it quits there!
Not sure how effectively I've been levelling my character - I'm putting quite a lot of points into Dexterity more than anything as it seems to up my attacks. Either way he's served me well thus far.