Gardens by the Bay had just been finished when I arrived in Singapore in July 2012. I count it as a “must-see” for anyone visiting Singapore for a few days. Its botanical garden is one of the most impressive I’ve seen in Asia so far, not so much for the specimens it has but for the domed, window-filled building that houses them.
The Cloud Forest is also worth checking out. The temperature inside is refreshingly cool, especially after you’ve spent an hour roaming about the massive metal “trees” outside. The Cloud Forest also has an excellent educational exhibit on how forests regulate temperature and their relationship with global warming.
Seeing everything only takes a few hours, if that. Most people will probably rush through it to check out the rest of the Marina Bay area, which has a huge sky-rise hotel, convention halls, the world’s largest roof-top swimming pool, a high-end mall, and a casino. But seeing Gardens by the Bay is about relaxing and slowing down to enjoy the splendor of nature, so it makes for a good escape before plunging back into the heat and the rest of your travels.