1. Black Park


2. Kew Gardens


3. Epping Forest


4. Cassiobury Park


5. The Upminster Windmill


6. Morden Hall Park


7. Trent Country Park


8. Eastbury Manor


9. Stocker's Lake Nature Reserve


10. Richmond Park


11. Ruislip Woods and Lido


12. Bentley Priory Open Space


13. Crystal Palace Park


14. The Chase Nature Reserve


15. Greenwich Park


16. God's Own Junkyard


For more off-the-beaten path gems in London:
CORRECTION
You should alight at Kew Gardens station to visit Kew. A previous version of this post mistakenly recommended Richmond.