What additions would you make to the Dark Brotherhood's torture chamber?

Be imaginative... and have fun.

the ability to actually torture someone?

the ability to put anyone i want in there (looking at you nazeem, delphine, and Heimskr)

The ability to remove it. The Dark Brotherhood is in the business of killing people, not extracting information.

There'd be like an iron maiden, but instead of nails, it would play actual Iron Maiden songs, but they would all be in the voice of the Adoring Fan.

A crystal chandelier, chocolate fountains, a sumptuous buffet, and a cocktail lounge.

M'aiq would convert it into his personal litter box chamber.

Nothing. I run the place, doesn't mean I have to be there for the day-to-day operations. Like the Thieves Guild, the Mage College, and any other supervisor position I hold in Skyrim.

Now, if you'll excuse me, I have a meeting to attend to because Imperials and Nords can't stop bickering.

I second this, and make it so if you release them, they remember what you did - not just completely forget and go back to normal.

A large feather to tickle my victims to death.

I never use it...I agree with the we kill people...not torture them statement.

A nuke to blow it to smithereens, and hopefully the rest of the sanctuary with it.