Just found Halloween decorations in Ul'dah (10X Y8) and I'm sure there's decorations in Limsa and Gridania. Go check them out :D
Edit: OH! there are missions! Speak to the people near the decorations wearing bikinis and you can start collecting what they ask for and receive a seasonal item for it.
Edited, Sep 10th 2013 7:18pm by OhimeKowai