Tangkoko National Park, around 2 hours from Bitung City. You can use cheap public transportation, but it will be very difficult as you have to change several cars. The most efficient and easiest way is to rent a car, which cost around Rp. 450,000 - Rp. 500,000 per day. Here you must stay one night, as there are many resorts and small hotels in this place. At night you can hire a guide to take you to the forrest to see the smallest primate in the world called as "Tarsius".
If a travel to Tangkoko national Park is impossible due to your time, there's a mini zoo in Bitung, only 10 minutes from Bitung's downtown. This mini park has collection of tarsius, birds, anoa, babi hutan, crocodile, etc. They will charge for your volunteeraly donation to feed those animals. Usually it's around Rp. 20,000 - Rp. 50,000 depending on the numbers of the visitors in your group.
Lembeh Strait: 30 minutes nfrom Bitung. It's a diving heaven for divers, but it's quite expensive, because the resort is managed by westeners.
