i kno the murrengreat hammer is in the heroes guild in the 20 key chest but u cant get to it because jack of blades blocked the doors with rocks so is there any other way to get to it?
no
You can use the walk through walls glitch to get through the face less demon door but it doesn't teleport you anywhere. It was originally meant to lead you to the dragons cliff but it was taken out due to deadlines etc...
No... In the Lost Chapters, they made it lead to the Fire Heart, which is needed to get to the Northern wastes. That's all it does. Lionhead Studios just probably saved it for the next game, to rip us off.