Mount Duff is the highest peak on Mangareva, rising to 441 metres at the southern end of the island. A trail to the summit takes about 2–3 hours return, through vegetation that changes character as you gain altitude, from coconut palms and breadfruit at the base to more montane scrub higher up. The summit gives panoramic views across the entire Gambier lagoon, the surrounding smaller islands, and — on very clear days — an enormous expanse of open Pacific.
Ask locally about trail conditions before attempting the climb — the path can be slippery after rain. The locals know the mountain well and can point you toward the correct trailhead, which is not well-marked. Bring water and sun protection; the upper slopes offer little shade.