Decide whether you want to get from Seattle to San Diego quickly, or whether you prefer a more meandering route. If you're in a hurry, you'll want to use Interstate 5 for most or all of your journey, but if you have time to spare, consider the winding, scenic coastal highways.
Take Interstate 5 south out of Seattle, and continue past Olympia (the state capital) into Portland, Oregon.
Stop in Portland to visit the Oregon Museum of Science and Industry, or carry on through the city to the "End of the Oregon Trail" interpretive center in Oregon City, a tribute to the pioneers of the Pacific Northwest.
Continue south on Interstate 5, drive through Grants Pass, and enter northern California near the beautiful Mount Shasta wilderness region. Or, drive west from Portland along one of the highways that leads out to the Oregon coast, and then drive south on Highway 101 along the coast of California, stopping at Redwood National Park to see some of the world's largest and oldest trees.
Connect with Highway 1 a few miles south of Garberville, if you want to take the coastal route, or stick with 101 if you prefer to drive through California's famous wine regions.
Continue south, either through Sacramento (if you're still on I-5) or San Francisco (on Highways 1 or 101), and head for Los Angeles. The inland route will take you through lush fruit and nut groves, as well as drier, more desert-like terrain, while the coastal route will keep you at the edge of the Pacific for the entire trip.
Stop in Los Angeles to visit Hollywood, Universal Studios and Beverly Hills, or attend a live taping of one of your favorite TV shows.
Head south on I-5 once again, following the signs to Anaheim (you may have to start on Highway 101 south, depending on where you are in L.A.), and spend some time at Disneyland or Knott's Berry Farm.
Get back onto I-5 when you leave Anaheim, and continue south to San Diego, via San Juan Capistrano. While in San Diego, don't forget to visit the famous zoo, or maybe spend a day at SeaWorld.
