The trip from Mount Rainier National Park to Seattle is only 85 to 95 miles from both park entrances but takes close to two hours to complete thanks to some twisty terrain.
From the Nisqually Entrance on the southwest side, follow Route 706 west for 35 miles until the road becomes Route 7. Continue north on Route 7 for 10 miles, and then turn right onto Route 161/Eatonville-LaGrande Road. Follow Route 161 north for 15 miles into Puyallup, and then take Highway 512 East to Highway 167 North. Follow Highway 167 North for 22 miles to I-405 south, which quickly heads west to I-5 in about 2.5 miles. Once on I-5, continue 10 miles north to Seattle.
From the White River Entrance on the east side, follow Route 410 north for 33 miles through Greenwater to the town of Enumclaw. Past Enumclaw, turn right onto State Route 164, which continues north for 7 miles through a hybrid of farmland and suburban residential blocks to Highway 18 in Auburn. Take Highway 18 west for 3 miles to I-5, and then follow I-5 north for 24 miles to Seattle.