Go 230 miles (370 km) due north of San Francisco and you’ll find yourself in Humboldt Redwoods State Park. Here, you’ll find the Rockefeller Forest, the world’s biggest old-growth forest of coastal redwoods. The state park is also famous for the “Avenue of the Giants,” an aptly named highway that features three redwood trees that are so massive that people carved tunnels through them, which you can literally drive through.