Hershey is very close to both Lancaster and Harrisburg and about 50 miles away from Gettysburg. I recommend staying in one of those places and visiting Hershey as a day trip. Also in the area are caves, shopping outlets, Amish country, parks, museums, good nightlife, etc.
.....its about an hour away but well worth the drive. I'm talking about Doubleday Farm - a bed and breakfast kinda place with a twist. The twist being baseball the old fashion way complete with the look and feel and of course a player from days gone by....
It's located in Landisburg, PA. From Carlisle, head north on Rt. 74 and up over Waggoners Gap (stop and take a look at the view there!) you will want to look for Pinehill Road.
There web site can be found at: