I'm still early on (in Forest of Fallen Giants), but I either came across an amazing coincidence or discovered a shortcut to the Cardinal Tower. It's going to be difficult for me to describe, but I'll try:
From the Cardinal Tower bonfire, I went down the ladder, through the fog gate in the room on the right, ran up the tree, fought the hollowed with their backs turned and took out the hollow that throws the fire bombs from above (where that Knight fight is when you climb the ladder). Anyways, in that corner before you go down the ladder to see Pate, I used an estus flask. After I used the flask the corner wall shatters to reveal the room where the Cardinal Tower bonfire is.
Has anyone else opened this shortcut or found out why it may have opened? I'm not sold that what I did was the only reason it opened up.
Yeah, a dude threw a firebomb in those barrels by the wall and they blew up taking the wall down. It scared the shit out of me, but was so happy with that shortcut :D