In this tutorial by Shooting Eggs, you'll learn how to create your own "ocean in a bottle". The supplies are very simple and cheap, probably stuff you've already got around the house. But the finished effect is pretty impressive.
A clear plastic or glass bottle
Blue food coloring
1. Partially fill the bottle with water.
2. Now pour the baby oil on top.
3. Finally, add the food coloring. Now you have your own private ocean in a bottle!