The right answer is "a small and unclean office ".
The answer to this question expounds, literally in the text. The excerpt that shows this is: " I was surprised to find the office spacious, neat, and clean. Somehow, I had expected to see a cramped, untidy, and dismal space."
Basically, the character is surprised to find a clean, spacious and tidy place, because he expected exactly the opposite, that is, a small, dirty and untidy desk.