The hike around the base of Mount Rainier is a multi-day endeavor. Since the author mentions a guide, I’d guess this is what they mean. It requires preparations like shipping supplies in advance- jeans would be a poor choice.
Author here... I edited "around the base" to "at the base." It was indeed a day hike. I originally said "around" as in "putzing around," not "circling around."
https://www.alltrails.com/trail/us/washington/the-wonderland...