@Stoori

If the door would indeed slide upwards, the wording would more likely be "dörren glider uppåt". The word "glider" contributes to confusion here I think, but it could just as likely be the door opening in a normal way (outwards from the wall), just more slowly and covertly. I had never thought about this much so it was an interesting question 😊.

Swedish is very weird sometimes. I can't immediately think of a similar use of "glider" in another context. Sometimes people "glider in i rummet" and it kind of signifies that they enter the room almost unnoticeably, or they do it in a smooth way. Can't really say out of context.