The California redwood, or Sequoia sempervirens, is legendary as one of the world's longest-living plants, with trees reaching ages of up to 1,800 years. One old-growth forest of California redwoods can be found just 19 kilometers (12 miles) north of San Francisco at Muir Woods National Monument in Marin County. Given how close the park is to the city, and also how impressive the giant trees are, Muir Woods can get crowded. If possible, timing your visit for early or late in the day is recommended. (The park opens at 8 a.m. and closes at sunset.) A boardwalk here allows those with limited mobility to experience the grandeur of the redwoods; others can explore several trails that head deeper into the park.