Near the top of the Crocker Range, next to the main highway, 20km north of Tambunan, this park is devoted to the world's largest flower. The Rafflesia Rangers can guide you into the jungle reserve for the day for RM100. Keningau-bound buses will stop here if you ask, but getting back to Tambunan will require hitching on the highway. A round-trip taxi from Tambunan costs RM120, which includes waiting time. Call ahead to make sure the reserve is open.
The rafflesia is a parasitic plant that grows hidden within the stems of jungle vines until it bursts into bloom, at which point it eerily resembles the monster plant from Little Shop of Horrors. It emits a stench of rotting flesh, mimicking a newly dead animal, to attract carrion flies that help with pollination. The large bulbous flowers can be up to 1m in diameter. The 12-or-so species of rafflesia here are found only in Borneo and Sumatra; several species are unique to Sabah, but as they only bloom for a few days, it's hard to predict when you'll be able to see one. Check with rangers at what stage the blooms are, as by day four they tend to be blackening and wilting.