O Le Pupu-Pu'e National Park protects a sweep of Upolu from inland rainforest down toward the south coast. It is the place to see the island as more than beaches: volcanic ridges, thick forest, birdsong, and trails that feel properly tropical.
Conditions vary with rain, and trails can be slippery or overgrown. Ask locally before setting out, and do not underestimate the humidity. The reward is a sense of Upolu's interior, where the villages and resorts fall away quickly.