Detailed mapping shows the "hot spot" that fuels Yellowstone National Park's geothermal features is more than 400 miles deep, and might have been responsible for volcanic activity in Oregon, Washington, and Idaho 17 million years ago.

There are times during the hardest of Rocky Mountain winters, when the mercury slides far below zero, that Yellowstone Lake’s heavy mantle of ice grinds and groans under the pressure of shifting flows. Snow can fall so deeply on Yellowstone National Park in Wyoming’s northwestern corner that workers at times must clamber onto the rooftops of lodges and cabins to shuck off the fluff so it doesn’t collapse the roofs.

For most, a national park vacation entails booking a room in a lodge or reserving a spot in a campground, arriving at the park and checking in, and then spending a number of days hiking, paddling, or traveling the park to view various sites, whether they focus on waterfalls, geysers, deep forests, museums, or cultural focal points. Here are some alternatives to that approach, some pricey, some not so.