Mount Rainier is a 14,410 foot volcano that can be seen from over 100 miles away in any direction.  The National Park is located in the west-central part of Washington State.  A day trip from Seattle might be tempting but I think a 2-day itinerary is the best way to see the highlights of the area.  The park's scenic drives and hiking trails not only give you great views of the volcano but also glaciers, waterfalls, alpine meadows, and old-growth forests.    

Model Itinerary

Day 1:

​The park's Nisqually entrance is 85 miles south of the Seattle-Tacoma International Airport.  Doing a day trip to the park from Seattle is possible, but I recommend planning for at least 2 full days.  There are only two hotels within the park, the National Park Inn in Longmire and the Paradise Inn in Paradise.  There are also hotels and cabins for rent in Ashford and other towns near the park entrances.  The park also has 3 drive-in campgrounds.  We stayed 1 night outside of the park at a camping spot in Ashford, and 2 nights inside the park at Cougar Rock Campground.
Day 2:

If the weather is good today head up to the Paradise Jackson Visitor Center where you can find several trail heads and check the park schedule for any ranger programs or ranger guided hikes.  Pack some snacks and water and head out to hike the Skyline Loop Trail (5.5 miles strenuous). We took the High Skyline Trail and followed the glacial path at the foot of Mt. Rainer up to Panorama Point.  There are pit toilets available at Panorama Point.  From there we took the Paradise Glacier Spur Trail to Myrtle Falls and Sluiskin Falls.  They say to allow 4 hours for the hike but since this is a strenuous hike we made frequent stops, including a lunch break at Panorama Point, stops at waterfalls, and stops to observe some marmots, so it took us 8 hours round trip.  Although this took most of the day, the trail lived up to its reputation of being the best trail in the park and ranks as 1 of my top 2 trails in any National Park.  (My other top trail is the Narrows in Zion NP).  The trail ends back at the visitor center and the park lodge where we were happy to go straight to the dining room for dinner!
Day 3:

Begin the day with a scenic drive to Ohana to see the oldest trees in the park on the Grove of Patricarchs Trail (1.2 mile easy hike).  These 1,000 year old trees are located on an island in the river which protected this area from forest fires.  You can access the river by crossing a short swinging bridge.  The scenic drive was designed to provide pull-offs at scenic overlooks with interpretative signs that tell you more about the area and what you are seeing.  Return to Paradise area for lunch and try one of the Ranger guided walks or talks in the afternoon.  In the evening, stay for the Night Sky program led by park rangers and volunteers.  Park Rangers set up 3-4 telescopes and we had the chance to see planets, stars, and even galaxies that were visible that evening.      
Day 4:

There are plenty of additional trails and things to do in the park if you have more time.  We stopped here for 2 days as part of an itinerary that also included Seattle, Mount St. Helen's National Monument, and Olympic National Park.