What is a must visit in the center of Phnom Penh for a day?

What is a must visit in the center of Phnom Penh for a day? If you have a day and want to visit the most attractive sites in the center of Phnom Penh here are some places you may want to visit:

1. Royal Palace. Landmark palace complex built in 1866
2. Tuol Sleng Genocide Museum, Museum in a former Khmer Rouge prison
3. Choeung Ek Genocidal Center, Infamous killing fields of Khmer Rouge
4. National Museum of Cambodia, Leading repository of ancient Khmer art
5. Phnom Penh Night Market, Fabrics, crafts &  snack stalls