This is a large, ornate, and extremely heavy chest.  It is made of dark wood, and has some rather disturbing scenes painted on the sides.  There are five faces carved onto the lid.  Many people will see it and instantly make the somewhat forgivable leap that it contains treasure.  It does not.  This is a good thing to afflict greedy, incautious players with.

In the dim past, a foolish necromancer summoned five demons from another plane.  They (or rather two of them) proved too strong for the necromancer to control.  He ended as a gibbering lunatic and killed himself.  The demons proceeded to run amok: ravaging the countryside, terrifying the masses, etc.  All efforts to banish them back to their home plane were completely unsucessful; the nature of the demons made it impossible to get too close to them.  A powerful priest, after a huge expenditure of effort, time, and money, created the Tanglewood Box.  It held some of the most powerful enchantments and blessings available.  The net effect was that those five specific demons were pulled into the chest, and once it was closed, held them there.  (There is a smaller, less powerful chest called Isheron that will bind demons, but will not pull them into it, as well as the less specific Blakrune, which pulls all demons (not just the five specific that the priest was aiming for) toward it and binds them inside.)  Once all five demons were imrisoned, the chest was hidden away under a mountain, and warded with extremely powerful spells, so as to prevent curious adventurers from opening it.

The Tanglewood Box was hidden away so long ago that the protective spells are wearing thin, and are no stronger than the spells in a typical dungeon.  A legend has arisen that the fabled chest contains a fabulous treasure.  It is only a matter of time before a party of adventurers finds it.  The spells involved in making the chest precluded the use of a lock.  The latch is not hard to undo.  You can obviously figure out where this is going.

If the box is opened, the five demons will escape. 
   They are:
- Mischief, who will play irritating pranks, and generally annoy people.  He is much like a poltergiest.  He is the weakest.  He is not intentionally harmful, however.
- Chaos, who abhors order, and will do his level best to make things as wild and unpredictable as possible.  The laws of probability turn into Silly-Putty around him.  If he gets extremely strong, the laws of physics may be repealed.
- Illusion, who is a master at her craft.  She will create illusions, hallucinations, mirages, etc.  She does not actually change reality; she merely makes it look like she has.  She is drawn to sources of strong magic, and if there is enough ambient magic, her illusions will begin to take on substance.  She does not realize this.
- Insanity, who is one of the only two emphatically evil demons.  She can do most of the same things Illusion can, only she can alter reality on a whim.  She is not above manipulating the others to get what she wants.  She exists to drive people insane, and the bigger the effect the better.
- Fear, who is undoubtably the nastiest.  He thrives on terror, and will use any means at his disposal to cause it, including possibly summoning more demons, raising zombies, etc.  He exudes an aura that draws evil and/or terrifying creatures (including the undead).  If it’s frightening, he likes it.

Mischief and Chaos will sometimes work together, and sometimes one or both will work with Illusion.  Illusion hates Insanity.  Insanity and Fear are lovers, and will almost always work together, as their natures complement each other.  All the others hate Fear.  If the players are clever and convincing enough, they can get Mischief, Chaos, and Illusion to help them tackle Fear and Insanity.  Mischief and Illusion can be reasoned with.  It is possible, but more difficult to reason with Chaos.  Fear and Insanity will not be reasoned with.  Each demon is capable of possession, and will use someone similar to their own nature as a host.  This makes Fear even more dangerous, as he usually goes for the despotic pyschotics and/or homicidal maniacs.  Once a demon is back in the box, it will be unable to get out for a very long time, due to being weakened.  It takes the effort of all five demons to get out of the box. 

Of course, once the box is opened, the players get to go put the demons back in.  Getting them in is simple, if not easy.  Someone merely has to hold the box open in the demon’s vicinity.  The demons will resist with all the power they can muster, but if the box is held open long enough, the demon in question will be pulled into it.  The demons can close the box if they are not in it, that’s why it must be held open.  It is much harder to capture a demon if its host is conscious.

Magical Properties:

The chest itself is not cursed.  But, as noted, opening the box releases the demons, which means that the players will have to go hunt them down and get them back in the box.  The longer they’re out, the stronger they get.  This sparked three successive campaigns (not adventures) when I used it.