Killing Fields of Choeung Ek
Cambodia has an extremely sad history and a recent history at that. The Killing Fields of Choeung Ek is a mass grave and one of the sites where over 1 million people were executed under the rein of Pol Pot and the Khmer Rouge. Of course it isn't a jolly outing but it's a really interesting and informative experience which hopefully helps visitors understand more about what the country and its people have been through. You're given an audio guide on entry that leads you around the site and explaining the significance of each spot and includes personal stories and accounts from individuals. The fields are a short tuk tuk ride from the centre of the city.
Tuol Sleng Museum of Genocidal Crimes
Another important history site is the Tuol Sleng Museum also referred to as S-21. The former high school was turned into a prison by Khmer Rouge throughout the regime from 1975 -1979. Inside the buildings you can see the purpose built cells made out of brick and lining the inside of each room. Another part of the museum explains the process of trailing the guards who worked in the prison and for the Khmer Rouge and getting justice for the people who were imprisoned here. One of the really shocking parts of the museum is the sign of security regulations (see picture) in the grounds which emphasises the brutality of the place.
Make the most of Sihanoukville's beaches
Cambodia isn't just history and temples. Like its neighbours it has some great beaches for the days when you just need to be horizontal for a bit. Sihanoukville is a great place to get a slice of beach life and relaxation and also acts as a gateway to Cambodia's islands.
Cycle around the temples of Angkor
Probably the most popular option to navigate around the temples of Angkor is by tuk tuk. To be different why not rent a bicycle instead. This will be slower but means that you can enjoy the backdrop at your own pace and stop and start as you wish. There's also something really satisfying and calming about riding past the all the chaos in the sunshine.
See the fireflies in Kampot
At night in the little coastal town of Kampot, if you're lucky you might be able to catch a glimpse of their resident fireflies. Tours run that take you out for a cruise along the river with the chance to spot them in the trees. One of the more obscure nature trips out there.
Party on Pub Street
In Siem Reap, head on down to Pub Street (yes that is what it's called) to hit up the many bars and unwind after a day of templing and culture. It's a vibrant place full of bars and restaurants including street food options and loads of tat for sale. Obviously a place like this has the not so desirable elements of being a touristy destination but it has a great atmosphere and is loads of fun.