My partner in crime had mentioned years ago about a "back entrance" to Kelly Butte via the I90, but today we climbed the actual trail. Views of Mt Rainier start from the trail head and just get better as you climb.
It is hot with no shade and there is a pathetic tarn once you get to the lookout... if you want to filter water instead of hike it in... I recommend hiking it in.
Kelly Butte Lookout is a first-come-first-serve campsite. There were 3 people relaxing from an overnight with nice views of Mt. Rainier, the I-90 Cascades and The Enchantments. The bugs were annoying once you stopped to take in the views, but not a problem if you kept moving.
This would be a great spring hike when all the Bear Grass is in bloom! ^_^