Well Cambodia is bordered with Vietnam, Laos, Thailand and the Gulf of Thailand, the geographical location testifies the cultural diversity of Cambodia. Well Cambodia has bustling and vibrant cities including Phnom Penh, the capital, Banlung, Battambang, Kampot and many more. If your trip is of 3 weeks then you should stay in each city at least 2 or 3 days. Well the capital city has a lot to offer including Sisowath Quay aka Riverside, Tuol Sleng Genocide Museum, The Killing Fields of Choeung Ek, The National Museum of Cambodia, The Royal Palace and many more. Well you should avoid any thing that is perceived against the local culture. Before visiting there you should know the basics of Cambodian culture to avoid any difficulty.