I first read about this meditation from Glenn Morris's book "Path Notes to an American Ninja." Though I think some of his ideas and philosophies are a bit hokey, this meditation has kept me entertained (even sane) on many long trips and other boring and mentally numbing times of my life. I'll try to sum it up the best I can without plagiarism. For a better version see the book above pg 73, meditations for creativity.

This meditation is aimed to increase your mental visualization and creativity. There is no particular posture or breathing necessary for this exercise as with some others, just find a comfortable position and begin to relax your entire body. This is generally not for beginners and many will have difficulty concentrating for a long period of time necessary to fully achieve this meditation. However, since it is one you constantly build on (not unlike any other long term project) you do not need to complete it every time, but get to a satisfying point and add every time. Sometimes it helps to picture the meditation like you would from the words of a good author or a movie. Also, these characteristics are interchangeable (I didn't like the graveyard bit so I changed it to an indoor pool). It's your world, create it as you wish. I'll explain mine a little better after.
To begin, imagine yourself emerging from the water next to a beach facing the shore. In front there is a hill leading away from the shore. As you walk, you gain power from every step digging into the sand and pushing off with power and confidence. As you climb the mountain ahead you notice an old abandoned temple and a graveyard which are in ruins. There are bathing pools still inside the destroyed temple that hold water. Continuing onwards the climb is more difficult. Touching trees along the way, you notice energy can be consumed through your hands as well as your feet. Ahead, the path diverges. You notice a welcoming path along one side and go towards it. At the entrance of the cave a cloaked figure stands guard, and gestures to you to enter and bows to you. You feel accomplished, like a king/queen of this cave.
You enter the cave, finding a long downward descending tunnel. The walls glow phosphorescent and give just enough light to lead down the path. Following further, it opens into a subterranean cavern that flows of red-hot lava on the far wall from the entrance. To the left is a pedestal with a leather bound book. The cover reads in flashing gold "All Knowledge is Power. Seeking Truth, First Look ye Here!" Behind this is another large room filled with an entire array of communications devices and computer setups. There seem to be three seats. One is yours, the other two belong to a young women and young man sitting busily at work. They haven't noticed you.
To the right is a great stairway of five steps, each of a different color slab in front of it. Doorways opened off of these slab. The first is
red and the door heavy and barred. You open it into a rugged, ancient desert. It reminds you of ancient Egypt. In the distance, there is a city built of stone. The second step is
orange and its doorway is a Dutch door. It looks out into babbling streams the flow through forests and end in magnificent waterfalls. They end in vast lakes and there appears to be a ship approaching. The third step is
yellow and the door is intricately cut from a large, single piece of solid oak. Through this door is a city that appears both modern and ancient. It is the home of man, elf and many other creatures living in harmony. You listen and hear music and laughter in the near distance, possibly a gathering. The following step is
green and opens to an open sky. There are birds floating, but withing reach of your hand. It's as if you are looking out of a high building window. The sky is cloudless and light blue. The last step is
blue and more spiral off into the distance in colors of v
iolet all the way to white.
Now that you have begun your journey into Da Mo's Cave, it's time for you to make your own cave. Maybe when you come out of the water it is night instead of day and there is a festival going on in the shore. I added 4 by 4 blocks of wood to make stairs up the mountain for ease of climbing. I generally don't stay outside much since I'm always adding to details of my cave, but you could always add other paths and see where they go. The cave seems safer to me and I even added a few more guards to the front entrance. Sometimes they are creatures, not humanoid. Inside your cave you can add beds, paintings and anything else you want. Add more rooms, that's what the extra colored stairs are for. Inside the room that leads to air, why not sour on the shoulders of some great beast, or just be able to fly yourself. I often dive into the lake and swim under the waterfall, or search for Nessy (the Locke Nest monster, I know it's strange). Make the incoming ship a pirate ship and party with them, or a submarine and go into the depths of the lakes. It is an exercise in creativity. This meditation is 1000's of years old and goes to the begining of recorded Zen teachings. Obviously, they didn't have computers. This is something that has been added by practitioners in common times. Add new technologies, or revert back to medieval days. Travel the world, or travel space. There is no limit, and nothing is wrong. Live out your fantasies. If you are skilled at meditation and can ignore the noisy distractions of daily life you can do it anytime. Plane and car trips work for me.