Northwest Gongsimdon is one of the distinctive defensive structures on Suwon's Hwaseong Fortress, built as a multi-level observation and fighting tower along the wall circuit. It is a detail stop, but a good one: the structure shows the fortress's blend of practical military planning and elegant Joseon design.
Include it while walking the walls rather than seeking it out in isolation. The tower helps break the circuit into memorable segments and gives context to why Hwaseong is more than a simple city wall.