Old Faithful is the name of a famous geyser in the Yellowstone National Park in Wyoming. Each year, huge numbers of people flock to see this remarkable feature of the natural world, with its regular eruptions of boiling water into the atmosphere.
In Walk Two Moons, Gram has waited to see Old Faithful for her entire life. At long last, she's now on the brink of making her dreams come true. Come the glorious day when she will finally set eyes on that big geyser, Gram is lying on her bed, staring at the ceiling. She hasn't had a wink of sleep all night, an indication perhaps of how excited she is at the prospect of achieving one of her life's goals.
In fact, Gram is so excited that, when she actually reaches Old Faithful, she crawls under the rope to get a better look at it. A park ranger politely, but firmly, tells her that she needs to stay behind the rope.
When Old Faithful has another of its regular eruptions of boiling water, Gram is most impressed. As the water shoots up into the air, she says it looks like “an upsidey-down waterfall.” At the same time, everyone can feel the ground rumbling beneath their feet.
All in all, watching Old Faithful turns out to be a very emotional experience for Gram. When everyone's in the car, ready to leave, she starts crying and sniffling:
I'm so happy I got to see Old Faithful.