Walk around Marina Bay and see the Spectra Light Show; explore Supertree Grove at Gardens by the Bay, open until 9 PM (note: light show usually starts at 8 PM).
Free entry, Gardens by the Bay conservatories extra approx. USD20 if visited, 1h30m
Explore key city sights including Petronas Twin Towers (photo stop), KL Tower (ticket included), Chinatown, and Merdeka Square with an included hop-on hop-off pass.