We have the Black Pits, which are great.
What about some player VS player action?
It would likely be different rooms with different levels. For example, "Level 5-7 characters only" all the way through to the higher levels. Also, to prevent people from having uber stats, there should be a stat point cap of 80 points maximum per character. No more.
Every player starts naked and buys a few basic items from the merchants before the fight (or, barring that, depending on the class, the character starts the game with pre-set items.) For example, a ranger could start with studded leather, a bow, and whatever weapon he chose in his proficiencies. Long sword, or spear, whatever. Kind of like when you start a new game in TOB, the starting items are attuned to your chosen class.
This would not only be fun, but it would enable players to learn from one another about the best way to manage combat tactically, either 1 VS 1, all the way through to 6 VS 6. What spells to cast and when, who to focus on first and why, micromanagement and party management.
Could there ever be something introduced like this?