Head North from Bilibin towards the icy mountains, and then west along them to reach Bilibin Cave. This serves as the challenge preceding Imil, where the story really kicks off. For now, though, you must navigate through yet another dungeon.
Bilibin Cave Entrance
This is the first place where Djinn will come into play as necessary to progress. Head North as soon as you enter the map, and you will see a small, leafy, green plant against a cliff wall. Once you're standing in front of it, switch Garet's Mars Djinni Forge with Isaac's Venus Flint to cause both characters' classes to change to "Brute". Brute has a crucial ability called Growth, which will make this plant work for you. Use your new skill to turn the little plant into a vine up the cliff wall, which you can then climb. Head north along the cliff, jump over the water, and then walk to the right side, where you will see a door. slide down the wall at the designated point and enter.
Now that you're done growing things, it's advisable to return the Djinn to their proper owners; Brutes aren't particularly good, and having two characters with identical skill sets is quite unnecessary. Later on, when you have more Djinn of all types, you can rearrange them to form many new classes with wildly varying abilities, but for now it isn't worth it to spread the different elements around.
Inside the cave, walk north, open the chest to gain the Elven Rapier, and then slide down the wall. Head as far left as possible, and then travel north along the wall. When you reach a split path, head right again. Go through the door you see heading north. In the next room, there's many ice pillars and water puddles; you can't do anything with them right now, since you have no Mercury (water) adept, so walk on by. Heading along the path, there is one of the ice pillars blocking the way. Move the fire torches near the Ice pillar and it will melt; Move them away from it, and the cold will reform it. Once it is melted, you can jump across the puddle. Walk down the newly opened path to the north until you reach the treasure chest. Get the contents, and then go back, exiting the dungeon through a opening in the south. Once you're outside, just walk to the west and then north up the peninsula to Imil.