Final Fantasy XI is well known by its players for providing unique holiday offerings. From the Taru-heavy celebrations of the Starlight Celebration to the Moogle-hunting antics of the Starbreeze holiday, Square/Enix has done a great job of taking real-life special events and tweaking them into Vana'diel-specific jubiliations.
June 27th marks the beginning of the Celestial Nights event, a sort of summer celebration of togetherness. In past years it's been marked as probably one of the most unique in-game events in any MMO because of one very out-of-game requirement. In order to succeed at the event, players have to write poetry. Real poetry, not clicking on an object and watching for a 'write poetry' cooldown. FFXIclopedia might just be able to answer some pressing questions about the event, with some lore text to lay on you as well.
Celestial Nights will be ongoing through July 8th, and you can talk to the Moogles in Northern San d'Oria (D-8), Bastok Markets (G-8), and Windurst Waters (F-5) for details on how to participate.