Morning:
Start your day to experience a cultural and historical site of Wat Phnom, the city's namesake temple located on a small hill. Enjoy the peaceful surroundings and observe the local worshippers.

Next, visit Wat Ounnaloam to learn about the important Buddhist temple in society amongst Cambodian people.

And after that exploring the Royal Palace complex, which houses the spectacular Silver Pagoda with its floor made of 5,000 silver tiles.

Then continue to see National Museum to learn about Cambodia's rich history and culture, with a focus on Khmer art and artefacts.

Seeing the independent monument which represents the freedom from the French colonial and head to see the statue of King Father Norodom Sihanouk a former king of Cambodia.

Break for lunch at local restaurant to enjoy a traditional Khmer meal.

Afternoon:
Visit Tuol Sleng Genocide Museum (S-21): this haunting museum, which was once a high school converted into a prison during the Khmer Rouge regime. It offers a sobering insight into Cambodia's tragic past.

After that going to Choeung Ek (Killing Fields): take a drive to the best-known of the Khmer Rouge killing fields, where you can pay your respects to the victims of the genocide and learn more about this dark chapter in Cambodian history.

Evening:
Shopping at a well known local market- central market- where most local and foreign tourists choose souvenirs for friends and colleagues. Afterwards to view sunset at Mekong Cruise that you can take a rest and relax on boat for a nice soft drink or beer with snacks, view sunset gradually and watch the beauty of the city from the river.

This itinerary offers a mix of historical, cultural, and culinary experiences, providing a well-rounded overview of Phnom Penh City in just one day. Adjustments can be made based on personal preferences and interests. Enjoy your tour!