You don't have to dive in this awesome place to appreciate its beauty. Lembeh strait is the best place to find corals and sea creatures, but its landscape has its own charm. You have to see it for yourself to understand what I meant.
To go here it takes around 1 hour driving from Manado: just head to Bitung, and go further a little bit. You'll find it's worth the effort all the way up and down the road once you get there. There are a several bed-and-breakfasts and resorts to accommodate you, as well as some diving group to assist such as Eco Divers. For more information, check: DiveTheWorld and North Sulawesi Tourism Promotion Board official site here.