My Personal Experience: I went to Phra Sumen Fort this year August 28, 2017, together with my sister. We went there to take a glimpse on the fort with park near to the Chao Phraya River. Going there is worth it even in our limited time to catch a boat- the fort will make feel like royal:) Phra Sumen Fort is one of the must-see place if you want cool tranquility and relax in the park.
Phra Sumen Fort
Built in 1783 to defend against potential naval invasions and named for the mythical Mt Meru (Phra Sumen in Thai) of Hindu-Buddhist cosmology, the octagonal brick-and-stucco bunker was one of 14 city watchtowers that punctuated the old city wall alongside Khlong Rop Krung. Apart from Mahakan Fort, this is the only one still standing. Alongside the fort and fronting the river is a small, grassy park with an open-air pavilion, river views, luscious trees, cool breezes!!