This is the oldest Hindu temple in Colombo, by most accounts. It's in a hidden location just off D.R. Wijewardena Mw and is a pleasant and welcoming kovil to visit.
Though the kovil is called the oldest in Colombo, a lot of the structures are new. The coat of paint certainly is, and they're building more off to the side. The main kovil that is a square around an inner sanctum.
Inside there's a simple but wonderful band playing (video above, click it), when we went just one drummer and one man playing a wind instrument. The main objects of worship at the temple are Easwaran (Shiva) and Ganesh, but there are altars and images of a range of gods.
Pay special attention to the ceiling which has beautiful painted images and statues.
It's a local kovil which people do come to worship at quite seriously, but they're also open to tourists and taking pictures (for a nominal charge).
The kovil is in an interesting location. On the map it's between the upcoming floating market in Pettah (near the bus stand, W.E. Bastian Mw) and the upcoming Lotus Tower (the circle on the map).
In reality, however, it's within a somewhat isolated loop with all the main roads some distance away. Most of the neighborhood is taken up by rail tracks. Despite being in the center of Colombo, the kovil is actually out there on its own.
Some kovils are less friendly to non-worshipers than others. This one is good for tourists or photo-happy locals. You simply pay a nominal fee to use your camera and then you can wander and click away.
Obviously you need to respect basic standards of dress and decency and not interrupt the people actually praying there.
The oldest kovil in Colombo is definitely worth a morning visit. It's in a hidden part of the city and is quite pretty and friendly.
Best early in the morning.