Located just inside the Alpine Lakes Wilderness, the Ira Spring Trail to Mason Lake is a relatively short hike in terms of distance, about six miles out and back. The elevation gain is what gets you on this hike - in only three miles the trail directs you up about 2,550 feet. It's a LOT of up, however the views at the top (seriously, amazing) and the lake itself make it all worthwhile.
The first two miles or so of the hike is honestly, rather unremarkable. However, continuing along you'll have amazing views of Mt. Rainer, the I-90 Corridor, and seasonal wildflowers. After three miles, crystal clear (and icy cold) Mason Lake is the perfect place for a dip after all that elevation gain. You can even make a night out of it and camp in one of the primitive sites marked around the lake.