From Seattle:
Most visitors to Olympic National Park fly to Seattle and rent a car for their visit. Getting to the Olympic Peninsula from Seattle is actually quite enjoyable, especially when you choose to take one of the Washington State ferries, which provide a relaxing ride across the Puget Sound.
To get to the ferries, take the airport exit road to Washington 518 East to US-5 North and exit the highway at 164B. Follow the signs to the Port of Seattle and the ferries. You may choose one of two routes that depart from this location – the Bremerton or the Bainbridge Island ferries. The latter run more frequently and the crossing is shorter but both are scenic.
You may also drive 17 miles further north on I-5 to Exit 177 and follow the signs for the Edmonds ferry to Kingston, a 30-minute crossing that puts you even closer to the attractions on the Olympic Peninsula.
From Port Angeles:
If you’ve flown into Fairchild Airport in Port Angeles, you’re already in the heart of the Olympic Peninsula. To reach the various attractions in the park, simply exit the airport on West Airport Road until you reach U.S. 101. Make a right to go to Sequim and points east or a left towards Hurricane Ridge, Sol Duc, Forks, the Hoh Rainforest, and points west.
It really is necessary to have a car at your disposal for exploring this national park. There is some public transportation to major towns on the peninsula, but nothing that will take you into the heart of the park to see the sights you’ll want to visit.
Sea-Tac Airport has a booth for just about every major car rental company and the Port Angeles airport has a Budget Rent-a-Car location on site.