Plants will have varying levels of people working on PLC's... this will depend on the plant itself, but can be a good introduction into how they work and provide exposure to PLC programs, topologies and SCADA systems.
To actually work with them, you probably would have to find a systems integrator... however, from my experience these will be small companies that may or may not treat the employees nicely. Also, there is for some reason an expectation that PLC engineers will put in overtime for free and work away from home without time off in lieu. This seems to be common between large and small companies by the way.
I would prefer to do that kind of work, but this attitude from companies completely puts me off. It may work with some people, but not with me I'm afraid.