[quote=Asuras]
I had knowledge of The Forest of Fallen Giants and Heide's Tower but that was it.I'm now sitting before the last boss (I think?), but I don't know how to get to it. I know it's there, but I just don't know how to activate the fight/get to the area.
[/quote]

Unless you've killed 34 other bosses(and that's just the ones that give you a unique soul) I doubt it's the last. I could be wrong, but I know there are 34+ bosses in the game, not counting mini bosses.