If you go by topographic prominence, meaning elevation of a summit relative to its lowest contour line, then Mount Rainier is actually greater than K2, the world’s second highest peak. Rainier is the most heavily glaciated peak in the contiguous US, smothered with 26 glaciers. Ice seracs the size of apartment buildings and crevasses that look like cities are an awesome and terrifying sight that greet climbers descending after a predawn ascent.
Rainier is normally climbed in two days via its easiest route, with the first day spent getting up to Camp Muir, at 10,080 feet, where there is a public shelter and a ranger outpost. Most parties camp here and then do a midnight summit attempt while the snow and ice are firm, taking 6-8 hours to get to the top. Due to the high altitude of Rainier, and the fact that sleeping up at Muir can adversely affect climbers coming up from sea level, it is recommended to spend the night before starting out somewhere on the flanks of the mountain or national park, as opposed to just driving up from Seattle, which can increase one’s chances of summiting by a lot.
Rainier is riddled with crevasses and steep ice and requires full mountaineering equipment and experience. For those who don’t have it, Rainier Mountaineering Inc has been leading successful climbs on Rainier and elsewhere in the world for over 40 years and their guides come highly recommended.