Having a large, gorgeous library in my home is a fantasy. I see beautiful wood paneling, shelves enclosed by glass, a podium, cases of ancient books with delicate pages, maps, ladders, stationery, a chaise lounge, magnifying glasses, large windows- it would be filled mainly with astrology, occult, psychology and metaphysical books.
I never connected the dots, until this morning, that a fantasy of an amazing library might be connected to having Neptune in Sagittarius in the 4th house, with Jupiter on the 8-9 cusp conjunct Mercury- that my fantasy (Neptune), involves my home (4th house), the accumulation of knowledge (Sagittarius and Jupiter), reading (Mercury), and occult/ metaphysics (8-9 cusp).
Neptune represents dreams and fantasies, among other things, and its placement can show what people fantasize and dream about- it can show what would be a dream come true for that person.