Sihanoukville is primarily a beach destination and so the main activity is laying around doing precious little.
That said, Ream National Park, and the islands of Koh Rong, Koh Rong Saloem, Koh Thmei, Koh Ta Kiev and Koh Russei are more rewarding than Sihanoukville proper.
Sunset and early evening on Serendipity are great crowd pullers, while Otres beach, with its bohemian vibe, is rising from the ashes of a recent bulldozing with new, hip accommodation and a popular windsurfing outfit. Diving, fishing and snorkelling options are plentiful in Sihanoukville and the surrounding islands.
Diving in Cambodia is reasonable and the areas around Sihanoukville are some of the better regarded in the country.
Five dive outfits in town offer training and certification as well as fun dives.
There's fish around them islands and a few local operators will help you get out and catch them.
Yes even windsurfing and kayaking has come to Sihanoukville.
Daylight ends around 6pm here, and the vacation continues. Many beach restaurants stay open until the last customer leaves. Restaurants with French, Japanese, Italian, Indian and many other cuisines come to life. Some bars and the casinos are open 24 hours a day.
Many close by stops await you outside downtown Sihanoukville. The fishing village at Stung Hauv, Kbal Chay Waterfalls, Ream National Park, day trips to the islands. You can even holiday in the coastal towns of Kampot, Kep and Bokor Mountain, just 2 hours away.
Many vacation activities around town are related to the beaches. Swimming and sunning, trips to the islands, fishing, and snorkeling. Within town, there are many themed restaurants and bars owned by people from all over the world. Buddhist temples, mountain biking, dirt biking, walking around downtown and the central market, shopping, and seeing the Cambodian culture are also popular activities.