We went to Indian Echo Caverns years ago - it was cool.
We really enjoy ZooAmerica which you can go to without entering Hershey Park if you are so inclined. If you have membership with a local zoo, check to see if there is a reciprocal entrance agreement; we have one with ours.
Troegs was really fun - their tasting room has a great menu; we ended up going there twice (snack on Friday, lunch on Sunday). My husband did the tour - it cost $5 and he got 3 samples plus a pint glass, good deal! I'm hoping to do it when we go back in October.
I have always been interested in Hershey Gardens but we have not made it there yet. It looks amazing.
I fifth(?) the vote for Chocolate World. Good to know about the trolley ride being fun; we'll put that on our list.