One of my favorite parks in suburban Yokohama is Maioka. This 28 hectare (69 acres) park is a blend between nature and traditional Japanese farming. It is citizen maintained and even has a school staff training program if you want to become a volunteer.
It is a long walk from my house, approximately 8.4 kilometers (5.2 miles), but well worth the exercise. Yes, you can take a train to Totsuka and a bus to the park or walk 20 minutes from Maioka Subway station to the entrance. This park is well maintained and has a thatched roof Meiji period house/museum (old Kaneko residence) that was actually relocated in 1995 from my home area Higashi-Totsuka. It serves as an educational center for traditional Japanese farming and has a large rice field where school students come and get their hands dirty planting and harvesting the rice under the supervision of volunteers. During the fall, the field is surrounded by quite colorful scarecrows, all hand made by the students.
I come here for the bird watching. Over the past 30 years there have been documented sightings of 122 different species of birds. I have found the good birding spots by following the birders to various locations around the park and then coming back to those same areas very early in the morning. As the saying goes, the early worm catches the bird, or maybe in the reverse, but it works well for me.
I take the beautiful walkway that starts near Maioka Blue Line subway station and first head to Kappa Pond, where I have seen several bamboo partridges. If you are really patient and focus your camera on the pond there are always frogs just at the water's edge. I then walk to Sakurana Pond area for the elusive kingfisher. Sometimes he sits and poses for me and other times he is too quick to catch a shot. It is not difficult to find a quiet area for bird watching away from the crowds, who tend to be found at the museum or around the rice fields. There are picnic tables, benches, as well as running water so you can plan on a day long outing.
There are trail maps throughout the park - do make sure to keep to the trails, though, as I have spotted a few viper snakes, and some ugly looking hornets. Mamushi, vipers, are a real peril in parts of Kanagawa Prefecture. For your exercise try some of the trials with stairways leading to the top of hills that surround the park.
This is a great place to visit as a getaway from the hustle and bustle of the city and to enjoy the great outdoors.