One of the Places we would go just to get away from it in Tacoma, Washington was Fort Steilacoom Park. It was just a nice wide open park with hiking trails, playgrounds, wide open fields, and many areas to take your family out for flying your remote control airplanes, and RC cars without have to worry about hurting people in the process.
As you hike around you can get plenty of exercise here. These trails go for very long distances. If your into hiking and nature. Or just want to get away and play with the kids on a wide open area. This place is nice.
One of the coolest things about this place is the very high trees. They remind me of very tall Christmas trees but, these huge pines as you stand underneath them all just make you feel so small.