Nyungwe National Park is approximately 225KM, from Kigali, easily four to five hours drive. While the road to Huye is good, there are many sharp turns and winding areas. The road in the park will take time to drive and you should allow yourself extra time.
Directions from Kigali:
Drive SW to Muhanga, then turn southwards to Nyanza, which lead into Huye, From Huye turn west to Nyamagabe which is very near to the National Park entrance.
There are a number of interesting historical sites to see on the way, such as Nyanza King’s palace at Nyabisindi, the reconstructed King’s palace which gives the insight into the royals of Rwanda Kingdom, the National Museum, intore dancers, crafts shops, the arboretum and the Cathedral all in Huya and Gikongoro’s Genocide Memorial along the way to Nyungwe.
The Kigali Rusizi Road cuts through Nyungwe National Park, this means you can easily use public transport to get here. The main road from Kamembe to Bukavu runs through the park, a few bus companies seem to run every two hours or so.
Most Travellers book through Tour Operators, however there are Self-Drive and Public transport options available.