By boat
Sunset Baan Tai and seaview to Ko Samui Ko Samui / Thong Sala
From Ko Samui: There are at least 3 ferries a day from Ko Samui's "Big Buddha" pier directly to Haad Rin. Ferries also leave from Nathon and Mae Nam piers to Thong Sala several times a day. Fast Lomprayah catamaran costs 300 baht (3 times a day), while Songserm Express 200 baht (twice a day).
Watch out for scammers at Ko Samui airport who try to sell you a bus/boat combo for an exorbitant price. Make sure to walk towards the exit of the airport where there is an Information counter and taxi stands.