How to locate CAN Bus "port" within a car

Generally speaking, where is the OBD / CAN Bus port/connector located in a car? Is it readily accessible, or does one have to break into potentially hazardous wiring territory within the car? (I'm not even sure if my car, or even most modern cars, have this kind of data provision.)

I tried looking in the manual, but perhaps I have got the terminology/idea wrong.

I've recently become interested in experimenting/learning more about this subject after having read about the CAN-Bus support on the Arduino Due.

Normally it is on the Engine Control Module or Powertrain Control Module, whichever they call it on your vehicle.

Noted -- and does one have to hack something apart to get access to either of those modules? I guess I'm asking how I actually break in to this area of the car.

Normally it is pretty easy to get to. Dealers and repair shops access it to check the ECM or PCM status for troubleshooting dashboard warning lights. It may have a dust cover on the OBD socket.

Thanks for the tips! I've also now located some information about it in the online manual/documentation pertinent to my car.