While you can explore Siem Reap, scramble temples, visit villages, and see the countryside independently, you'll get more out of the experience and gain an insight into local culture if you do a tour with a Cambodian guide. Don't just wander into any travel agency. They may all promote tours but often these are little more than an over-priced tuk tuk ride with a driver who only speaks Khmer. Of the countless tours on offer these are my favorites. All are operated by responsible tour companies.