I'm in Act2 of the game, but I've found one in Act1. You can't really miss it, as you have to go through that area to get the bag. I believe it's the small area with 3 keys, a transportation pyramid (not the ones you get in Act2, but the one that transports you when you touch it, and you can't pick it up.), and a little more to the north is the bag on an altar kind of thing.
Tovi 
