The Jardin Botanique de Cayenne is a small but pleasant tropical garden at the eastern end of the Avenue Charles de Gaulle, next to the university. Founded in the 19th century, it preserves examples of useful and ornamental species from across the Amazon and Caribbean — cocoa, breadfruit, cinnamon, kapok, royal palms — and offers a shaded escape from the city heat.
It's not a manicured European-style botanical garden, more a research collection that survives in a half-wild state. Free to enter and unstaffed; the garden is at its best in the cooler mornings.