Take a bus to Mt Rainier.

This is just in :

On July 20, Mount Rainier National Park will become the official owner of a vintage 1937 Kenworth Touring Motor Coach. Historic bus returns to Mount Rainier
This coach transported visitors to Mount Rainier between 1937 and 1962 from the historic Winthrop Hotel in Tacoma and Olympic Hotel in Seattle.

Sweet Classic Ride

According to Mt Rainier Park officials : "The park plans to have the coach on display at various times throughout the summer".
So, I guess, you can't take that bus to visit your favorite park. That's too bad, because it's a pretty sweet ride. It’s got the old original engine, a stick-shift tranny and the most fun part - the whole top folds back. According to the owners, Art Redford and Frank Pupo of Gig Harbor, the “coach” is one of only five built by Kenworth between 1937 and 1938. Two others still remain active – one in Sitka, Alaska and one in Montana.

Many out-of-state visitors often ask me this question :" How can we get to Mt Rainier, if we don't have a car ?"

Well, one option -take a Gray Line of Seattle's scenic bus ride from downtown Seattle.
It's not just a ride. Along the way to the Park, they stop at several scenic lookout points. Back to Seattle they a different route, taking in even more great scenery. The price ? $ 62 + tax. Big disadvantage - tours are offered from May 1 to September 30.

Another tour operator- Seattle Tours offers same- day trips to Mt. Rainier in one of their clean, comfortable 24-passenger mini-coaches with large windows, high back seats and air-conditioning. One big plus - door-to-door service from downtown Seattle, SeaTac,Tukwila and Bellevue hotels, hotel’s specific pick-up time. Cost- $88.58 plus tax

This tour operator is on the bottom of the price list, but at the top of service providing. Yes, you will pay $ 185, but you will get much more for your money.This full day retreat, with Evergreen Escapes, to Mt Rainier glaciers,waterfalls and wildlife offers ample opportunities for adventure, exploration, learning, and just plain having fun ! Your naturalist mountain guide will lead you out on a short hike or snowshoe along the Nisqually Vista trail or possibly something a little more challenging. Advantages : pick up- city hotels and cruise terminals
season- spring ( snowshoeing !) and summer

And finally ! The winner !The money savor ?! FREE National Park Service Shuttle from Ashford to Paradise !
Drawback - getting to Ashfod. Couple options:
•Ace Taxi: 253-589-1000; Round trip transportation between SeaTac airport and Ashford.
•Yellow Cab Inc: 253-848-2930; No airport pickup but available for return trip to SeaTac from Ashford. Also available to pickup anywhere in Tacoma area.

Hoenstly, I haven't had a chance to use the shuttle and can't vouch for it, but it's in my plans. For more information about the shuttle, call 360-569-2211.

Other than that, unfortunately, there is no public transportation to Mount Rainier National Park.