The playground at my elementary school had no fence. On one side of the building there were frogs and turtles, by a water source (can't remember now if it was a small pond or a creek), and on the other, forest. Our play equipment was there under the trees. We would swing high to try to touch the branches of the trees, and throw stuff up into the trees, climb trees, play hide and seek. As long as we came back when the bell rang, we could wander free. This was in the 80s. I was 1st/2nd grade. After 2nd grade they closed the school down and combined us with the main elementary.
I take that back - there may have been a chain link fence way at the back of the property. But that didn't stop the boys.