The easiest thing to do is enter 223 Battery Way, Port Townsend, WA 98368 into Google Maps for exact directions from your location.

Via Car from SeaTac Airport

Non-Ferry Route:
From SeaTac airport, you can drive south, via I-5 S to Tacoma, and WA-16 W and WA-3 N to WA-104 W. This route takes approximately 2 hours, 10 minutes at best, and can be congested during rush hours.

Ferry Routes via Car:
From SeaTac, drive to the Downtown Seattle Ferry Terminal (Colman Dock) or the Edmonds Ferry Terminal. Ferries to Bainbridge Island, Kingston, or from Victoria B.C. and Whidbey Island will get you to the Olympic Peninsula.

• From Victoria, British Columbia via Victoria/Port Angeles Ferry:
  Take the Victoria-Port Angeles ferry (90-minute crossing). Ferry exits onto Laurel St .2 miles. Turn left onto E. Railroad St. 0.1 miles, take 1st right onto N. Lincoln St./US 101 E. and continue for 34.2 miles. Turn left onto WA-20, go 7.8 miles and turn left to stay on WA-20 for another three miles and you have reached Port Townsend.
• From Vancouver, B.C. via Whidbey Island – Port Townsend Ferry
  Follow Provincial Route 99 south to border crossing. Provincial Route 99 S. becomes I-5 S. Go 46.1 miles take exit 230 toward WA-20/Burlington/Anacortes. Go .4 miles turn right onto WA-20 E. make a U-turn onto WA-20 W. Go 11.8 miles turn left onto WA-20 and continue 16.4 miles turn right to stay on WA-20, go 9.5 miles turn right onto S. Main St. go 0.6 miles (S. Main St. becomes Engle Rd.), go 3.3 miles. Take the Port Townsend-Keystone Ferry. You are now in downtown Port Townsend.