Yellowstone rewards slowness. The temptation is to drive the Grand Loop Road ticking off geysers and hot springs, but the park is best experienced by stopping often, lingering at viewpoints, and getting out of the car wherever the landscape looks interesting. Plan for at least three full days — a week lets you start to understand the place.
The thermal features and wildlife are the two great draws, and fortunately they often overlap: bison graze within sight of steaming hot springs, and wolves hunt across valleys where fumaroles vent in the background. The Lamar Valley and Hayden Valley are the best places for wildlife; the Upper Geyser Basin and Midway Geyser Basin for thermal features.