Going to Monrovia already puts you off the beaten path, but I understand that Delta is soon going to initiate a direct flight from the USA so maybe this is not far enough off for you. If you looking to go further off the path go upcountry. This is not to be recommended to the stiff or arthritic. More of the road is paved then was the case in 1976, but the pot holes are awful. They reminded me how I came to prefer dirt roads. They will only get worst during the rainy season.
Now if you really want to suffer try going by road all the way to the eastern tip of Liberia (Cape Palmas). Most of this is still dirt road. This is where I worked as a Peace Corp Volunteer 34 years ago. I was told by several people that it could not be done. I think this is an exaggeration. It might take three days and multiple different "taxis", but I believe it is doable. Perhaps just not practical, tolerable or worth the suffering. I plan to prove it on one of my future trips to Liberia.