VNC Connection to from one system to another routed through third system in between

Question

I'd like to set up a VNC connection to a system, which is only connected to another system in between via a private network, essentially the system to be connected has only a single network connection to the "middleman" computer (which is connected to the outside world).

Using my computer on different network, I'd like to set up a desktop session to view and monitor the target system. I suppose this would imply turning the "middleman" system as some sort of router, to forward the request, with the VNC server resting on the target machine, and a client on my own system.

I'm not sure how to do this, I'd like to try this with SSH tunneling as an addition.

Is this possible, and if so is there a step guide somewhere which I can use to get started with this. I'll be using TightVNC, or if any other VNC exists which makes the process easier, that'd be fine, too.