I've lived in Prince George my whole life and have done everything that CAN be done regarding fun.
Most people who come here don't look into these things and will come for the trails and hiking, which is beautiful of course, but there is so much more to see.
Prince George has one of few drive-in theatres in Canada. It is some-what of a drive out of the Hart area, but it is awesome! There is a concession that sells very good food and even mini-golf and go-karting out there.
Roll-A-Dome! This is another thing many cities don't have. It's old, yes, kind of run-down... but it's SO much fun! You can rent old school skates or bring your own rollerblades. It's great for birthday parties, too! I've had many there, myself.
Almost nothing to do in Dowtown Prince George. Avoid it !
Stay in the wild countryside around the city !