librejo

Decode it and the meaning is inevitable.Libro is a book, -ej- is the suffix for the place where something happens or is kept, and librejo is therefore the book place. The suffix is one of the most productive in the language and it is worth collecting the pattern here: lernejo a school, preĝejo a church, kuirejo a kitchen, vendejo a shop, dormejo a dormitory, panejo a bakery. Learn -ej- once and you get a hundred nouns free.

Which is exactly where the trap is, because English has two book places. A librejo is a bookshop: you go in with money and come out with a book that is yours. A lending library, where the book goes back in three weeks, is a biblioteko, and that word is a separate Greek borrowing rather than a build. English library and Esperanto librejo look like the same word and are not, which puts this beside novelo and aktuala in the false-friend file. If you want to be unmistakeable, the language gives you librovendejo, book-selling-place, which nobody can misread. A bookcase, by the way, is a libroŝranko.

One date to use it on. The Esperanto movement keeps 15 December, Zamenhof's birthday, as Zamenhofa Tago, and the UEA pairs it in its own annual message with la Tago de la Esperanta Libro. The custom, as the Esperanto Vikipedio actually describes it, is an exchange of gifts, preferably books written in Esperanto, and the honest reason it works is that the date falls ten days before Christmas. So the sentence you want in mid-December is mi iras al la librejo. Festoj kaj la kalendaro has the full calendar, including which parts of the book-day story stand up and which are folklore.