What should be done with 20 year old college textbooks?

I know they are worth about 10–15 cents per pound in heat if I burn them in my stove.
Does anyone want old college textbooks? Isn’t everything found online now?
The books were so expensive when purchased 20 years ago but now they seem like boat anchors. Should I discard them in the recycle bin?
The library says they do not want old hardcover textbooks so I can’t even donate them.