Who knew?! About 50 feet back behind our property we have this! Yesterday the kids wanted to go out hiking with their father and they decided to head back into the woods. It's been a (very) weird winter. Normally the ground is marshy back behind our property, but it's still somewhat frozen - so it was easy to go back farther into the woods than the kids normally would.
With the kids starting to get a bit older maybe they'll start exploring more this summer... crazy! :) (Grandma Julia: The problem in the summer is marshy wetlands are ideal for mosquito breeding. That is what has kept me from exploring more with the children.)