There is currently no hotel or private accommodation near the airport or in the wider area.
Even for early morning departures, it is therefore worth staying in the centre of Siem Reap, from where you can always find transport to the airport, either by taxi or bus.
Accommodation prices are very reasonable and even a nice local hotel offers a room for 1 night from 25 usd.
Near the bus station towards the airport we recommend accommodation in Sinaka Angkor Hotel ***.
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