Kahuzi-Biega National Park
Most of Kahuzi-Biega is lowlands and is occupied by the FDLR (Interhamwe), those responsible for the genocide in Rwanda, and so is most emphatically not safe to visit. That said, you will be stopped by MONUC or local security forces on any road into this area long before you get to the park. The small highland section is open for visits, with three gorilla groups habituated for visitation.
The park consists of two sections, the lowland (closed for visits) and the highland (open for visits).