On 6A in Brewster, just east of the Cape Cod Sea Camps, is an old house with a 1/2 mile trail that leads to the ocean.
The main trail is short and steep down to Mystic lake but if you go right at the split it will bring you under Race Lane by way of an old cow tunnel.
Maple Swamp Conservation is 770 acres of land in Sandwich off the Service Road. It has some of the tallest and steepest hills on Cape Cod which then give great views out over the Bay.
The parking area is only a fews spots on the side of the road in Brewster but the trail brings you past a stone foundation form the 1870s, holly groves, and tall pines to one of the best views of Cape Cod Bay.
The Punkhorn Parklands in Brewster have many interesting walks but Eagle point has some of the best views.
Find yourself stuck in the middle of Hyannis looking to go for a lunch run, with solitude, check out Hyannis ponds. It's a Large patch of land sandwiched between Mary Dunn Rd, Rt 6, Willow St, and the Airport.
In the middle of Pleasant Bay there is a 75 acer island with trails, beaches and marsh creaks to explore.