My kids love Green Park in London. No playground equipment, but lots of trees (chestnuts in the fall) and paths to run down.

There are several stately homes in England with great playgrounds featured as part of entry price. The ones that come to mind are Longleat, Bowood, and Wilton House - all in the Bath/Stonehenge vicinity. Bowood has some slides and high-wire type climbing that still give me nightmares, but they are very unique, I must say.

In Singapore, Jurong Bird Park has a wet/dry playground which features lots of splashing. The only way to go in Singapore, with its sticky climate. Sentosa also has several play areas.

Hong Kong Park ( near the Victoria Peak tram station) has a walk-in aviary (don't know the status of this in light of bird flu) and play areas scattered about.

Tivoli in Copenhagen has a nice playground area with giant slides, trampolines, and unique playground equipment.