Tux is universal

Another thing that would be interesting is hedge mazes. Toss in a couple spots with that one-way paint and maybe some secret passages (some non-dense walls, right-click able ground that reveals a tunnel, etc.)
If there's a big pond/small-lake, have boats (though that may take a bit to implement unless they are not controllable and just follow one of several set courses).
Of course, you'd also have to have fishing in that case.
A park would also need a field for whatever sports get played in Hydlaa.
Finally, there should be a big honkin' sandbox for the youngsters, and maybe some treehouses (with ziplines between them?)