Cache near SihanoukVille city. Exactly at the end of Otres beach.
Otres beach is still the quiet, hard to get to beach, but it's started to boom.
This beach starts at Queen Hill resort, just over the Otres river at the end of South Ocheteaul Beach. This is the closest part of the beach to town, and you can walk from South Ocheteaul Beach, over the bridge to Queen Hill and then down the hill. Most take the new road, behind the "golf course" for a 10 - 15 minute ride from town. About $1.50 by motorcycle taxi and $5 by tuk tuk (for a few people in the tuk tuk). Best to get back before nighttime if you're not staying at night, as there are no lights on the road.
Info from: www.sihanoukville-cambodia.com