I walked downriver to Monas on Saturday. Jakarta is built at the mouth of the Ciliwung River, which forks at Manggarai just upstream from Halimun. Historically — I bet — Menteng is the area between the two rivers (canals, now), upstream from Monas.
The advantage to hiking along rivers (and train tracks) in Jakarta is that there are few red lights and little traffic. The downside is that the level of pollution in the rivers is depressing. This time of year, when the rivers are zippy, it’s no big deal. There was even a red-beaked water bird (foul?) doing flip-flops one after another near the bridge on Jl. Raden Saleh.
Walk through the totally bizarre but well-ventilated Cikini Market, cross the Ciliwung on the ancient foot bridge (I’m told this is where the train used to cross) and see if you can follow the east bank to the Jl. Veteran and the Fisheries Ministry. (You can, but you have to walk through somebody’s house!)