While I was looking to find the district office of Samphanthawong, I at first misread the map and only looked directly at the rim of the Chao Phraya river. Though I could not find the office there, I instead found a beautiful historic building, which one most easily can see when traveling on the river with the express boat. From the street it is a bit hidden, while the gate marking it a Siam Commercial Bank office is easy to notice, the building inside the compound is hardly been seen.
From the website Tour Bangkok Legacies I later learned that this building was built 1906–1910, and was designed by the famous Italian architect Annibale Rigotti (1870-1968). The same architect who also designed the Hua Lamphong railway station as well as the Ananda Samakhom Throne Hall. When finished, the building became the headquarter and first branch of the Siam Commercial Bank (ธนาคารไทยพาณิชย์), which was established in 1906. Until 1971 the headquarters remained in this location.
Later in 1983, the building housed the Thai Bank Museum, which however was moved into the new headquarter building of SCB in 1996 as well. Yet I think this building would be a much better location for such a museum, both easier located for tourists than the bank headquarter in the northern outskirts but also more fitting into this historic building than a normal bank branch office.
In case anyone is wondering where all the money deposited at the bank is going - at the entrance of the compound is the most beautiful ATM I have ever seen, housed in a small building in same style as the 1910 building.