Sunda Kelapa Harbour in North Jakarta (aka Kota) is well worth a visit, there is always plenty of things going on. Sunda Kelapa harbour still has plenty of these old pinsi ships loading and unloading lumber from Sumatra and Kalimantan and returning with fuel and concrete materials.
The sailors still unload most of them by hand, walking up and down precarious wooden planks.
You can hire a small canoe to paddle you around the larger ships, but watch out for the water, it is black and filthy. If you ask nicely, they may allow you on one of their ships, I had my 8 year old son with me, so they did for us!