How to open gate between Witches Horn and Swamp of Sacrifice

You can't ever open it ... but later there's another way through the gate. I won't say more b/c you will figure it out on your own. But that's not the way you're going to enter it the FIRST time, there is a different cave after you get out of the swamp. Keep looking, there is a path (a really fun path) to get out of the Swamp of Sacrifice.