Ngurah Rai International Airport, Denpasar: Sidemen has no useful public-transport link from the airport. Pre-book a private driver through your accommodation or a reputable local operator; allow roughly 2–2.5 hours (longer in afternoon traffic) and about Rp500,000–700,000 for a car. This is better value and far less hassle than negotiating an airport taxi for a remote, multi-stop rural drop-off.
Padang Bai ferry harbour: For arrivals from Lombok/the Gilis, arrange a private car onward from Padang Bai. Sidemen is roughly 1–1.5 hours away, depending on the exact valley hotel and traffic; expect about Rp350,000–500,000. There is no train station and no dependable scheduled shuttle worth planning around.