Persona 4 how to unlock Naoto Dungeon

About dungeons ...

Dungeons are themed around various character's inner selves (not sure if that applies to ALL of them, but the ones we've seen so far are).
Accessed from a television set (it looks like they use a big plasma screen in a store because their home tvs are too small to go through).
Yes, there are supposed to be traps. They haven't mentioned specifically what kind. Also, I think I heard something about there being locked treasure chests.

A quote from an interview:

Q. About halfway though Persona 3 I grew tired of the random dungeons, what have you done this time around to better the experience?

A. We're still using random dungeons, but we've done a bit with these missing people that you need to search for in each dungeon. There are certain themes for each dungeon that have their own accompanying challenge. To better improve the tempo of the game we've gone through and reexamined the overall volume of a level, filled them out as much as possible while slightly reducing the size, and a bit of tweaking by reducing gameplay time by a slight amount. That, and beyond the fact you can now exit a dungeon at any point with a specific item or magic, progress through a level is saved so you can start over again at any point.

Also, unlike Persona 3 where dungeons where mainly just for exploration, this time around there's also Event Dungeons where key pieces of the story unravel. On top of that, after you've completed a dungeon there's other elements to look forward to as well.

And that's about all I know / care to look up.