1. It’s within the largest ecosystem of its type in the world. 2. Super-heated pools of water, steam vents and geysers attract visitors galore, some three million tourists a year. 3. Yellowstone National Park is in the western state of Wyoming. 4. Yellowstone National Park is a giant swatch of terrain. 5. Extremely hot water shoots out of the ground in several hundred places. 6. Yet for all you can see, the real story behind Yellowstone is in what you can’t see.