What should I do with outdated encyclopedias?

I'm cleaning off the bookshelves in my parents house and we have found a number of books that we would like to get rid of. Most significantly, they have a full set of encyclopedias from 1963 and a full set of junior encyclopedias from the same time period, both in very good condition. Although the information is outdated, I hate to throw them in the garbage or recycle bin if there is some better alternative. Is there anyplace that takes this sort of material? Or is there some other option other than recycling them? Thanks for your help!