The Rain Forest Trail at Mt. Rainier National Park, WA, is an easy 0.3 mile loop hike located on the northwest boundary of Mt. Rainier National Park.
It's extremely short, but it's a really nice loop trail that gives you a quick peek into Rainier's rain forests.
You'll find that most of the trail is made up of large wooden planks to keep you off the wet ground.
Along the east side of the trail you may find a waterfall hidden in the back; however, I'm not sure if it exists throughout the entire year or if it only exists during the spring or after a heavy rainfall.
Also beware that there's a parking fee for the park and dogs are not allowed on any of the trails within the park's boundaries.