Like an obscure fiction book you love but have never heard anyone mention and maybe it's because it has a really off-putting cover? Or a non fiction book that's to do with a hobby you have zero interest in but the book captures your imagination anyway?
I think my favourite is Jane Asher's Fancy Dress. Jane Asher (ex girlfriend of Paul McCartney, not sure what else she is known for) makes fancy dress costumes for her celeb friends and family to model. My favourite is the jellyfish costumer that is literally an umbrella covered in bubble wrap and trimmed with metallic streamers. Or maybe Terry Jones as a topless girl with papier mache boobs jumping out of a cake... I found it in a charity shop and it has survived several bookcase culls, because I can't part with it!