Go to the caves, through the red sigil into the cave, down and then through the blue svirly thing (you will get a manapotion from it to teach you that you can drink them yourself and you need to do so to proceed).
The next cave will later be over the water stream and the third costs 500g and is not implemented yet.

Also when you get to size 3 you need to talk to the trader girl that will appear in the first cave area to get through the boulders.