I don't like to get my awesome vintage playground news from crazy, old post-war magazine articles about those crazy foreigners making fortunes from their crazy gadgets, but in this case, I'll let it slide. So to speak.
The Nazis chased sculptor Egon Möller-Nielsen out of Denmark, and a generation of Swedish playground denizens have been thanking them ever since.
Starting around 1949, Moeller-Nielsen created wild, biomorphic concrete play sculptures like Tuffsen, the cave/castle below, which was [is?] in Reimer Holm Park in Stockholm.
And The Egg, which went into Tessinpark in 1951, is obviously still going strong in 2007, as Jaime Silva's flickr stream proves.