I'm wondering, aside from the myriad of dangers, the risks of getting lost/eaten or otherwise wind up in some charlie foxtrot, how hard is it just to open a way to the nevernever?
Harry specifically says that it's not something he could do easily. Even in the more recent books the effort seems to tire him out quite a bit. Or it's implied anyway.
So how many shifts of power would be needed to open a way?
Also, is that done with a ritual or with a special kind of evocation?