(photos look better when the sun is shining :-))
A great recreation area in Vienna: In the center of the park there is the Danube Tower, where you have a good view while you wine and dine high up in the clouds. There is a mini train, bungee jumping stage, lots of play grounds for adults and kids, tiny animal park, etc....
And best of all: close by there are a handful of nice caches!
For information and a map see http://de.wikipedia.org/wiki/Donaupark_Wien
also http://www.wien.gv.at/ma42/parks/donaup.htm and http://www.wien-vienna.at/blickpunkte.php?ID=900