The Drunken Lizard Pub

I have really enjoyed the many hours I've spent with this game. I'm getting towards the end of the main quest line, and looking to the future, I find a growing sense of apprehension. You know, what I am I going to play after it's all over? What game could possibly offer me more of the same kind of ...

I'm having trouble figuring out how to cast portal. I mean, I seem to be able to cast it, but how do you jump back to that point you have "anchored"? Enlighten me, please. Thanks. (I'm loving this game by the way. Just found the invisibility spell!)