Hi Tony,
I've been down to Plymouth a few times in the last few weeks on maintenance runs.
I don't know Plymouth City (town?) itself, the last time I was there was around twenty years ago when I was about seven years old.
Just a quick warning: If you're landing on Runway 31 then try to stay high on the approach, especially over the factories on very short finals... the turbulence can be quite bad if you're on the correct approach slope. R31 slopes up...
The longest I've been there is around two to three hours (whilst a 50 hour check has been performed on the aircraft) but was utterly bored within an hour or so. Thus I took a walk and found a college and sports centre on the airport road and a little further on a McDonalds, Pizza Hut and KFC. All nice eateries... NOT!!!
On the otherside of the runway is a nice pub I've been told.
The town probably isn't far and there are a load of buses, or alternatively phone a taxi firm from the airport terminal.
Best wishes,
Charlie Zulu.