[kerkeslager]

I'm quite adept at visualization, as I'm a visual learner (visualization comes more naturally to me than any other form of thinking) AND visualization is something I regularly, explicitly do in order to prepare for rock climbing.

Visualizing myself going through a doorway is difficult even for me. I think it's in part because it requires some creativity (compare "visualize yourself going through a doorway" as opposed to "visualize yourself going through the doorway of your childhood house"). The salient conceptual feature of a doorway is that it goes somewhere and so the prompt basically is asking you to imagine something without explicitly asking you. Even your example of the basement stairway is much easier for me to visualise, because the doorway has stairs after it.