From West Yellowstone travel east on 20 to Madison Junction then south towards Old Faithful Village. Firehole lake is between Lower Geyser Basin and Midway Geyser Basin. From Jackson and the south take 89 North to West Thumb Junction then west past Old Faithful Village.
I don't know what had their attention as a small geyser was going off right behind them, but I liked their shared attention.
Bison doing what they do best, looking impressive and unperturbed. There are so many great wildlife viewing opportunities in Yellowstone but the bison seem to capture the spirit of the park.