You can bring your mountain bike or just walk the myriad of trails of this beautiful Sandy River Delta Park in Troutdale. You can bring your dog or your horse. Wonderful place to get lost in nature! Just be aware of the dog poop that can be in the middle of the trail or in a baggy thrown off the side of the trail. Can be stinky, but once you get further away from the parking areas you end up seeing (and smelling) less doggy doo.
The park is easy to get to, just off I-84, exit 18. Good for wildlife viewing as well! Bring your binoculars!