If you were to pick 2 sites in Colombo and like wrecks, do the Cargo Wreck and the Medhufaru Wreck. Both around 20 mins boat ride, easy profiles, intact ships of 90-100m in length and good fish life. The Basses has good diving but getting to them can be complicated. No dive operators in Kirinda (the closest town). Some dive shops from Hikkaduwa organize special trips but you have to book ahead for the whole trip usually or else its local divers organizing a trip. I might be there with my dive club in April but not confirmed yet. If, (and thats a BIG IF) the trip happens and the dates coincide you are welcome to join us. To be honest trying to do a day of diving on the Basses might be tough. Just visit Yala and if you have time do a few more dives somewhere else where there is a local dive shop. Btw try to visit Yala on a weekday. Its a great park but has become terribly overcrowded and is worse on weekends when you can expect 20 jeeps parked around a leopard!!!!!