If you have time go for a trip to the other side of Bangkok. You can see there a different way of life, crocodiles instead of dogs by the houses, fishermen, rural everyday life. You can spend there a few hours and watch around.
Very quiet place outside of city center. There are mostly trees, I wouldn't call it a garden, but it's a natural pretty place pleasant to visit nonetheless.
Seriously one of the most fun kayaking trip I've ever been on. Not extremely difficult at all but still a little hard for a first time kayaker or canoer.