Everyone who rides around here is really riding around one object. Mount Rainier is a stratovolcano of roughly 4,400 metres that rises out of the Cascade foothills with nothing of comparable size near it, which is why it dominates the sky from Seattle on a clear day and why, from up close, it seems to have its own weather. Locals call it simply the mountain, and they say it with the tone people use for a moody relative.
The road system on the park's eastern and northeastern side is built for looking. It climbs through dense forest of fir and cedar, breaks out into meadows, then tucks back under the trees, so the mountain appears in short surprises rather than one long reveal. Corners are broad and easy, the gradients are gentle, and the surface is usually fine. What costs time is not the road but the stops, because the viewpoints are good enough that you will make more of them than you planned. Riding it in the cool early hours gives you empty tarmac and low light on the glaciers.
The geology is worth a thought while you are parked. Rainier is active, and the Cascade volcanoes sit above the subduction of the Juan de Fuca plate under North America. Glacial meltwater runs grey with rock flour in the valleys, and old mudflows, called lahars, have filled valleys downstream with deposits that tell you what the mountain is capable of. The park was created in 1899, one of the first in the country, and the forests you pass through have trees that are many centuries old. In summer the high meadows carry lupine and paintbrush in numbers that surprise people who expected only rock and ice.
Be realistic about practicalities. Entry to the park is paid, services inside are limited and seasonal, so arrive with a full tank from the towns on the outside, such as Enumclaw or Packwood. Weather can erase the mountain completely, so if the forecast is poor, treat the ride as a forest drive and be glad of the dry, quiet corners. If the sky does clear and you get the summit alone against blue, you will understand why people plan whole trips around waiting for it.