On The Road To Bilibin
Note: If you have not yet completed your tasks in Vault, you will not be able to pass through the cave because Ivan won't follow you up there. Please see the section above for more information.
From Vault you want to head east. Keep heading east until you cross the bridge, and from there you want to start heading north. Keep progressing this way until you find a cave entrance. Make your way up the ladders until you get to a gap with a tree stump covered by leaves. Your psynergy isn't going to help you for this one, so try jumping over. When you try this, Garret comes out and tells you that your Psynergy isn't going to work. By totally random coincidence here comes Ivan who will blow the leaves off of the stump thanks to his new rod. He now wants to join your quest, and you're back in command. Now, move the stump, jump across and use Ivan's Whirlwind psynergy to clear the leaves at the gate to get in the cave.
In this cave you'll find a lot of ghosts and skeletons which aren't too tough. Primarily, you should use group attacking Psynergy that hits multiple enemies at once (like Ivan's lightening attack.) Inside the cave head up until you get to a stopping point (as in a cave wall.) Hop over the stepping stone there and head down. Next, head up the stairs and through the door. Head down the stairs and to the right. Here you'll see a traveler on the ground a Djinn on a ledge. Push the wood tree stump as high as it goes and so that it's in the middle of the two ledges. Now, head back from whence you came (3), but instead of going back up the staircases, head south and hop across a small stream. Continue along the path going through the various doorways. Eventually you'll get to a stepping stone that you'll want to hop across and to the other side. Go up the staircases and start ledge hopping. When you arrive at a ledge with a large tree stump, use Move to push it to the right. Hop onto this ledge then the ledge to the south, then Move the stump back to the left. Hop over and then over and to the right to obtain the treasure chest. Make your way back from whence you came (up to 4) and get back to the ledge surrounded by water. Go to the stepping stone to the right of the stairs, hop across and go up the stairs there. From here jump across the stump that you placed earlier to get a battle the Mars Djinn on the ledge. This Djinn is harder than your normal enemy, but he's not too tough. Use your existing Djinn on him, and also use your lone summon plus Psynergy attacks to beat him pretty Handily. Once he's defeated you will obtain this Mars Djinn, Forge. Head back to the ledge with the staircases and proceed upwards. You'll see a stump blocking the ledge that you have to hop to, so use Move to push that into the water. Hop across, go up and across the bridge and at the end of the hallway you'll be out of the tunnel. 3 seconds of moving right later and you'll be in...