What are some cities that have:

- high # of parks / public spaces per sq km
- walkable, public transit
- pleasant climate

 starting with ones Ive been to and liked:

- Singapore
- Vienna, Austria
- San Francisco, USA
- Brighton, UK
- Washington D.C. USA
- Hong Kong
- London

creating and destroying; flying cars, roc.camera, july.rocks /july /faust

Taipei. Not really deep forest parks (though those kinda exist in the north), but there's a series of rivers with a really nice ~43km long trail along them

I second the recommendation! 

There’s an abundance of trails in Yangmingshan national park—a volcanic mountain connected to Taipei in the north. 

Also an extensive network of wild hotsprings!