Basically, you are heading for the Hypostyle, which is the conclusion of episode 2. The portal to the Hypostyle is behind a gate inside the temple on Shadow Wood. There are three panels on either side of this gate. Each of the three pairs of panels have a different symbol: the Swamp symbol (green), the Horn symbol (yellow) and the Cave symbol (grey).
Each panel corresponds to a switch somewhere on this episode which you must activate, and the symbol on the panel indicates which key is needed to get to the switch. So, there are two switches which need the Swamp key to get to, two switches which need the Horn key and two switches which need the Cave key. Every time you activate one of the six switches the corresponding panel will brighten up. This way you can monitor your progress in solving the puzzle.
Once you find all these switches, the gate opens, and you will enter the portal to the Hypostyle.
Here's how to get to the temple on Shadow Wood and see the six panels: follow the left wall as you come out of the room where you start. Go through the doorway on the left and go up the stairs. This is the entrance to the temple. Go inside the temple, turn right and go to the end of the corridor. Open the metal wall on your left, and go down the corridor behind it. This leads to the room with the six switches and the gate. Since you haven't solved any puzzles yet at this point, the six panels will be dark (you need to walk up to a panel to see the symbol on it if it hasn't brightened up yet).
OK, that's enough introduction. Time to actually solve the puzzles. Since you need the three keys in order to get to the six switches, you have to first find the keys.