Thanks to Diane Baker, founding partner at Worn Jerabek Architects in Chicago, for telling me about the Japanese architects Arakawa and Gins and their marvelously innovative "Reversible Destiny Lofts" homes for elders in Tokyo.

You can read more in this 2006 story. Here is an excerpt:
As the title suggests, the housing itself is meant to reverse, or at least postpone, the physical and cognitive changes that often occur in old age "...by making you defend yourself against them" (Doctorow, 2007, p. 1). The living space has color, texture, and floor plans that keep residents vibrant by challenging them. Floors in some rooms are grainy, textured, and concave; the door leading to the terrace is deliberately so low that the elderly resident must stoop to go out on the terrace; and electric switches are intentionally placed in unexpected locations, "...so that you have to feel around for them"

Maybe our playgrounds could be called "Reversible Destiny Parks" ?

One of the earliest playgrounds for elders in Europe was built in Rovaniemi, Lapland, Finland. It was a collaboration between a manufacturer of playground apparatus and a university. This paper describes the efficacy of the experiment, http://is.gd/v2aPB7. Perhaps more illuminating, take a look at this video, http://youtu.be/N3HYYp7J3DQ. It’s almost too good to be true. Then again, maybe seeing is believing.