The diving in Sulawesi is fantastic, all from boats, and aside from some 50 local sites in the Bunaken National Park, there are also the joys of Lembeh if you want to dip your toe into the muck diving capital of the world.
When diving in Sulawesi the visibility is generally good, the coral is in excellent health and the fish life is primarily macro - you don't come to this part of Indonesia for the big stuff. This is where you can most likely find critters such as frogfish, blue ringed octopus, pygmy sea horse, mimic octopus…the list goes on.
Away from the water you can go on day trips to see the world's smallest mammal, the Tarsia, white-water rafting and various other activities but all mean a trip to the mainland and therefore a day trip.
One of the beauties of diving in Sulawesi is that, unlike many parts of Indonesia, it is easily accessible as there are regular direct flights from Singapore. This means that it can get very busy in the summer months but time your trip right and you get accessible, world-class diving at a great price.