The Manoa Falls trail is one of Honolulu's best free attractions — a 1.6-kilometre walk through dense tropical rainforest up a narrow valley behind the University of Hawaii that ends at a 46-metre waterfall dropping into a shallow pool. The forest is lush even by Hawaii standards, with ginger, guava, massive tree ferns, and wild orchids.
The trail is muddy after rain — wear shoes you don't mind getting dirty, and go prepared for a shower whatever the forecast says, since the valley creates its own weather. Mosquitoes are present; repellent is worth bringing. The car park at the trail head charges a small fee. The Lyon Arboretum, a botanical garden at the mouth of the valley, is worth an additional hour if you have it.