We have always gotten most of our outdoor time and exercise by living in a walkable neighborhood with public transit. My son and I commuted together when he was 2-5 years old, taking 2 buses each way, so that was lots of time walking to and waiting at bus stops. We would look at things both natural and human-made, and sometimes while waiting we played games like Red Light Green Light or danced--for a long time he wanted to act out the story of Cinderella with dancing at the ball.
His preschool had outdoor recess totaling 2 hours a day (he was there all day while I was at work) and although it was a very tight, urban playground, my son often spoke of natural phenomena they noticed: things fell from the trees, birds and squirrels and bugs were seen, clouds were interesting. In summer they got to play in water sprinklers.
Since he started kindergarten (now in 3rd grade) we walk to school every morning regardless of weather. There's always something interesting to see! His dad walked over to meet him after school until the middle of 2nd grade; now he walks home by himself or with his friend who lives nearby. A lot of kids stay and play in the schoolyard for up to an hour after school, and my son is among them. There's a playground, but he usually doesn't go over there, in favor of running around in the lawn and paved area in front of the school. They play elaborate pretend games, or tag, or have contests to see who's fastest at climbing over the low wall. Right now they are enjoying Leaftopia, where the custodian put all the autumn leaves into the low part of the yard surrounded by a fence so that they have an ENORMOUS pile of leaves to frolic in. There's also the Edible Schoolyard garden, where the kids can graze on raspberries and cherry tomatoes in season, and observe the changes in the plants.
He and his dad join some friends at the nearby park after school every Friday for about 2 hours. They mostly play on the playground but sometimes investigate the forest or creek. When my son was smaller, we took him to this or the other neighborhood playground about once per weekend for about 2 hours.
For us, a trip to our church, the supermarket, or the public library is a 3/4-mile walk each way, and this becomes an outdoor adventure. It's mostly built environment, but that means retaining walls to walk on, traffic-crossing buttons to push, pizza-tossers and tailors and hairdressers at work behind their windows, guys repairing wires, and other excitements. There are seasonal changes in the plants, even though these are domesticated plants in landscaping. There are birds, squirrels, bugs, cats, and dogs. There are other people to observe, sometimes friends to greet. I feel like we live on Sesame Street.