All-day summer activities for a couple in their 50s?

What are some good activities in the Central PA area for a couple in their mid-50's? I'd like to give my parents a gift for their anniversary that will conveniently take them out of the house for several hours (five or more) so that my boyfriend and I can have some privacy. They approve of the boyfriend, we're not sneaking around, we just feel more comfortable when they're not within earshot and not in danger of accidentally intruding. We live near Hershey, so anything within an hour's drive is good; things around Philadelphia might also work because we have relatives there. My parents are pretty low-key and simple, but they do appreciate fancier things. Activities can't be too strenuous because my mom has a knee replacement. They both really like dogs and 60s clic rock music, but otherwise their music tastes differ. I'm kind of at a loss for things for them since they don't have a lot in common and they don't go out and do a lot of stuff together.