As a real estate agent, I see multitudes of properties that have "extra space" that could be used for play or recreational purposes.  Houzz.com is one of my favorite sources for ideas that are all things renovation or makeover.  After living in Santa Fe, NM for 10 years, this fairyland forest basement makeover resonated with me.  It could a fun idea for any of those "extra space" areas your property or any property might have!