Cougar Mountain Park
Cougar Mountain Park has an extensive trail system. There are nice, wide trails that are used by both people and horses, and little, narrow trails for hiking only.
The main trailhead is just outside of Bellevue, actually in or near the town of Newcastle.
It's not really off the beaten path, in general, as this park is pretty popular, but it is off the beaten path of suburban Bellevue : )