The landing point places you in front of a towering and mysterious holed stone that stands upright alongside a paved road. If you follow that road to the Northwest, it will lead you to a bridge that connects the continent to a lighthouse. Go into the lighthouse, and follow the spiral stairs to your right up to the very top. There, you will find a clue that will guide the next steps of your journey. Without that clue, when you go back down to the very bottom of the stairs, you will find your way blocked.
Once you make your way through the wall at the bottom of the stairs, you will find yourself in a very long corridor. Walk straight ahead, and keep walking, and keep walking still...until you find yourself in a cavern beneath the earth, with your way again blocked. This time, a short pillar to your left holds the key to unlocking the door. The photo below is an aerial shot that gives you an idea of just how long that corridor is, and offers a clue to your final destination. (The lighthouse is the object in the top left of the photo.)
If you can unlock the key to that next door, you'll find yourself in a series of caverns filled with underground pools. One of these pools has hidden rooms beneath it; try to find your way down beneath the water to collect the treasure. Come back up, then behind the red couch is a short corridor that leads to your way out. Look around before leaving, because there are several more shiny and interesting treasures you can collect.
Unfortunately, I couldn't figure out how to get that last door open. (I had thought it was the "mythical femur" lying beside the door, but it doesn't seem to be.) If you can figure it out, let me know! Those who do figure out how to get out will find themselves exiting a fairy tale somewhat backwards - going from the belly of the beast to his mouth. I do hope you enjoy this Mainland adventure. After all, as Tolkien said, "it simply isn't an adventure worth telling if there aren't any dragons."