Formerly the site of a sugar factory, Santi Chai Prakan Park is now a tiny patch of greenery with a great river view and lots of evening action, including comical communal aerobics classes. The riverside pathway heading southwards makes for a serene promenade. The park's most prominent landmark is the blindingly white Phra Sumen Fort, which was built in 1783 to defend the city against a river invasion.
Named for the mythical Phra Sumen (Mt Meru) of Hindu-Buddhist cosmology, the octagonal brick-and-stucco bunker was one of 14 city watchtowers that formerly punctuated the old city wall alongside Khlong Rop Krung (now Khlong Banglamphu but still called Khlong Rop Krung on most signs). Apart from Mahakan Fort, this is the only one still standing.