**Warning to anyone reading you doesn't want the solution given away**
Here's the solution. The first thing you want to do is make it rain, so pick up the slate, and go to the stand with all of the symbols on the wall behind it. On the floor in front of the stand is an upside down slate. Draw the symbol you see on it, drop the slate, and walk away from it. The creature will appear and call down rain. If you approach the stand, you'll notice that water is pouring through holes in the top of the stand. This water is filling up bowls, which represent the turning stone things on top of the cliff. Once the rain stops, the bowls will be filled with water. Stand directly in front of the stand, and you'll notice the water in the bowls are reflecting 4 of the symbols on the wall. Draw on some paper which symbol represents which turning stone. After that, go climb up the ladder.
Now, since the symbols you have for each turning stone isn't on the stones themselves, you need to figure out which of the symbols that are on the turning stones go with the symbols you have. To do this you need to go to the big rock in the middle and open windows. Looking through the windows, you can see that symbols are printed over each window, but can only be seen from a window on the opposite side.
This'll take awhile, but you need to figure out which window each of the symbols you have is printed over. Once you've done this, the symbol on the front of the window which you can only see when the window is closed corresponds with the turning stones. These are the symbols you need to adjust the turning stones to.
Once you've done this, the turning stones will have opened up the tunnel that was blocked underneath the cliff. Go through the tunnel and that is the end of the demo.
I hope I haven't missed anything, as I just finished the demo a few moments ago after downloading it earlier this morning. If I have then hopefully someone will correct me. Have fun!