There is too much to do at the Expo park. Three hours is not enough. So many beautiful plants, education and cultural activities and a stunning aquarium.
The merlion is considered the emblem of singapore, and maybe my white whale. While I may have missed it I did get a chance to visit the beautiful Esplande theaters even if briefly.
There's tons to do at Changi Airport if you've got time to kill or just want to walk for a bit after your flight. Including a cool free light show in the evenings.