You could also go to a library and hunt for interesting books together. Libraries are not always crowded. Infact you could even call the library near you and ask them when their slowest time normally is and then plan to visit during that slow time. You have already said how you both love books.

Also can you check out Antique shops around where you live, sometimes they have old books and are not very crowded to go to.

I don't know where you live but if you live near the water, you could take a drive along the shoreline and look at all the homes etc and the water. I have done that with my husband when I just want quiet time.