Northwest of Seattle and Langley on Whidbey Island, the Metcalf Trust Trail System has a 10+ mile horseback riding trail network open to hikers, mountain bikers and horseback riding.
To reach the trailhead from Seattle, take exit #189 off of I-5, just south of Everett. Follow signs for the Mukilteo/ Clinton ferry. Take the ferry to Clinton on Whidbey Island. Follow SR525 northwest for 2.5 miles. Turn right on South Langley Road (aka Schneider Road) for 3.5 miles into Langley. Continue northwest on Saratoga Road for 1.5 miles to the trailhead.
Overall, Metcalf Trust Trail System is the 4th most popular horse trail of all 32 horseback rides in Washington.