Past the beaches there is a gilded Buddha on a causeway islet, an inland waterfall, a marine park an hour offshore and an elephant sanctuary — nearly all of it needing your own wheels or a booked transfer.
Samui Elephant Sanctuary
Two sites on the island, at Bophut and Chaweng Noi, running three-hour morning and afternoon visits plus a shorter 90-minute encounter, with no riding or bathing. Current website-booking rates at Chaweng Noi are 2,900 baht for adults and 1,400 baht for children aged 5–11; book ahead on 095 269 8343.
Wat Phra Yai (Big Buddha)
A large gilded seated Buddha on a small island linked to the north-east corner of Samui by a causeway, free to visit and open through the day. The pier beside it is where boats to Koh Phangan leave, so it works as a stop on the way to or from the ferry.
Mu Ko Ang Thong National Marine Park
An archipelago of limestone islands roughly 30 km west of Samui, visited on day boats that leave in the morning from the island's north and west piers. The national-park entrance fee is charged separately from the boat ticket, and trips are cancelled outright in bad weather, so book a day you can afford to lose.
Na Muang waterfalls
Two falls in the interior off Route 4169: the lower one is a short walk from the car park, the upper needs a steeper climb. Entry is free, there is no charge to swim in the lower pool, and both are worth far more just after rain than in the dry months.
Hin Ta and Hin Yai rocks, Lamai
Signposted off the ring road at the south end of Lamai, a short paved path through a gauntlet of souvenir and coconut-toffee stalls leads to two rock formations named for their unmistakable resemblance to human anatomy. Free, takes fifteen minutes, and the coast either side is good for a walk.