In Hong Kong, pre-handover, I stayed in a windowless hotel room.

I love to sleep in darkness. Stayed at an Airbnb with a windowless bedroom. Best sleep I ever had.

Second, would pay extra for that

Have you guys tried blackout curtains?

Those still exist in Hong Kong today. And many other places in the world, for that matter. Even apartments without windows aren't that uncommon. In subdivided floors they're cheaper than the street facing ones, but some people prefer them anyway because there is less noise from the road.

I stayed in one in london last year. It was great until noisy people came back at 2am

2 great sleep killers: light and noise. "Windowless" only fixes one.

Well, we're calling them "donut holes", but they're actually rectangles. :P

Don't be such a square!