The cable car ride up to the bastille is no Disneyland amusement, but it affords you some nice views of the city. I would actually recommend taking your grandparents with you, as I did, because their enthusiasm for pointing out things can be slightly contagious and makes the whole thing seem like less of a waste of time.
If you're planning a trip to Grenoble, I offer you this advice: the bastille is worth a visit I suppose, and if you really like big hills I'm sure you'll have a great time. Personally, I don't get that much enjoyment from looking at stuff from high up, but it was a nice enough walk. We had some good tartines for lunch.
Sorry about the horrible graininess of the photos - I am incompetent and had to mess with the light levels before the mountains were actually visible in a lot of these. I wouldn't have bothered but the mountains were sort of the whole point, so.