Actually, there used to be a swimming pool at Old Faithful, way back when (click to see a picture). It was furnished with hot water from Solitary Spring, which because of the lowered water level is now Solitary Geyser. The pool and its building were closed in 1949. If you want to watch some really interesting videos about Yellowstone, including the cultural history of the Old Faithful area, here is a link from the National Park Service.
I'm glad they didn't try to use Grand Geyser as the hot water source for their pool.
Grand is the largest predictible geyser in the park, over 200 feet in one or more bursts (I was lucky enough to see five bursts on my first viewing). Doesn't this make a terrific time travel device? See what I mean about inspiration in funny places?
So, I am going to go visit my muse. I promise to say hello for you [g].