Sapo, Liberia's only national park, is a lush 1808-sq-km tract containing some of West Africa's last remaining primary rainforest. Within it lurk forest elephants, pygmy hippos, chimpanzees, antelopes and other wildlife, although these populations suffered greatly during the war.
It's located in the Sinoe Province; you'll need to take a 4WD from Monrovia to Greenville, then head north to Juarzon and then southeast to Jalay's Town. You'll need to allow at least a full day's travel to here from the capital.