The bike path runs from Woods Hole to North Falmouth (11 miles each way, 22 miles total) with great ocean, farm, and marsh views.
Woods Hole is a great place to walk around and explore. Grab a coffee at Coffee Obsession, a pastry from the French Bakery, check out the Woods Hole Oceanographic Institution (WHOI) Visitor Center, take a swim at Stoney Beach, watch the ferries leave for Martha's Vineyard and enjoy the awesome little shops on Water Street.
The Knob is about a one mile nature walk (round-trip) with great views.