1. A place, or "emporium" if you will, full of fantastic items or pleasurable activities.
2. Used sarcastically to describe a place that is not fun or excitng.
Note that it is usually followed by a one or two word description.
1. Dude, I can't believe you don't want to go to the fair, it's a fantasmagorium of sight and sound!
2. (sarc.) Yeah, right I would love to go to Jeffrey Bacon's house, it's a fantasmagorium of fun and excitement.