Room Thirty

...room number Thirty. "What a beautiful door...the others are so plain," said one.
"It's meant to influence our decision," said another.
"Perhaps this has been done so we will not choose this door," said the thoughtful one.
They wanted to know what the letters meant. Obviously they meant something, and we said so.
"Yes, but...why 'O' and 'U'? What special significance can they have for us?"
The more confused they became, the more we enjoyed it. No matter how many times we've been through this we're always fascinated.
Leaving the room and all that it contained behind us, we entered...

...room 42.
...room 34.
...room 5.
...room 15.