I love old books. I love the kind of old books you get at antique bookstores or on the Internet Archive. And I have a good collection of old books about Denmark.
I like old travel guides, most of which are still pretty useful because Denmark doesn’t tear a lot of things down the way they do, in say, Los Angeles or Hong Kong. In Denmark you’ll pretty much fine most castles and monuments right where somebody left them hundreds of years ago.
If you want to see a famous church or square or the Jelling Stone, your Baedecker guidebook from 1895 will work just fine for you in most cases.
But I can also recommend two great old books on Denmark, which you can probably find at your local antique book shop, or on DBA, the Danish auction site owned by eBay.