Floating on an industrial canal which connects to the Beira Lake, Pettah Floating Market has a good collection of eateries, cafes and shops, and chairs for relaxing. It is a good spot to take photos of the Nelum Kuluna, also if you are waiting for a train from the Pettah Station, you can hang around in the market.
It is a popular place for local couples to hold hands, and stroll on the timber decks. The Floating market consists of 92 stalls selling various items like shoes, bags, t-shirts, junk jewelry, etc. The food is really cheap when compared to other malls like the Arcade Square. It is a good hangout place if you want to stop for some quick food while touring around Colombo, or if you are waiting to catch a train from the Pettah railway station.
The green waters of the canal is notable, and if you have the time try out the swan catamaran. However for foreigners, if your schedule does not permit a lot of time, you are not going to miss much if you skip this place.