Including Potts Basin in the north, Yellowstone National Park's West Thumb is the largest geyser basin that shares a border with Yellowstone Lake. The volcanic caldera that feeds the thermal features of the area (only 10,000 feet below ground!) is about the same size of Crater Lake in Oregon. It is, however, much smaller than the greater Yellowstone Caldera that sits over much of the park, which surrounds the West Thumb caldera.
The thermal features are not only on the shore of Yellowstone Lake, they are under the water as well! In the summer these are seen as visible cones underneath the shallow water along the shore, and in the winter you can see the heat melting a hole in the surrounding ice that can reach over three feet thick.
There is a short nature walk along the shore of Yellowstone Lake and among the geysers that give unique close-up views of the colorful sulfuric thermal features. Please stay on the trail, as people have been burned when falling into the springs and geysers.