So I placed the Vessel at the altar below the Firelink Shrine.
Except the creature spoke WAY too fast about where to actually go to fight the last four bosses in the game - so...the only one I can remotely identify is Nito, but all I can do is ride the coffin to his lair and enter his pact - how do you actually fight him? Does anyone know the locations of any of the other souls required?
The only one I know of is the Four Kings boss in Old Londo.
I'm having the same problem. There's one boss under the place were you ring the second bell, the hell fire place or w/e. After you beat the boss down there, the lava turns to rock and you can go down there to access one of the bosses. I just don't remember where the other doors are that opened.