By boat[edit]
Cruise boats run up the river from Bangkok, often stopping at Ko Kret and Bang Pa-In along the way. You'll need to book in advance as there are no scheduled services, just trips for tourists. It's a fairly lengthy trip (at least one whole day) and some of the larger boats offer (pricy) overnight tours.
Travelling by boat to Phra Nakhon Si Ayutthaya is popular among foreigners since it does not only reveal the beauty as well as lifestyle of the people on both sides of the Chao Phraya River, but also reflects the life in history at the time of the Ayutthaya Kingdom when the Chao Phraya River served as a channel of transportation in trading with foreign countries