Translation:The desk is next to the bookcase.
"Το γραφείο είναι δίπλα στη βιβλιοθήκη." Translation:The desk is next to the bookcase. The sentence as you can see from the top of this page is correct.
The desk /γραφείο is next to the bookcase /βιβλιοθήκη "desk" and "bookcase" are both kinds of furniture so it's logical that they can be next to each other. So you have:
furniture=>desk /γραφείο and furniture=>bookcase / βιβλιοθήκη
On the other hand, you could also have the "office /γράφείο is next to the library/βιβλιοθήκη.... in this case an "office" is a room/or building and the "library" is also a room or a building so this too is logical.
room/building => office/γραφείο and room/building=>library/ βιβλιοθήκη
Two possible English sentences for the same Greek sentence:
"The desk is next to the bookcase" or "The office is next to the library". Also possible for the same Greek sentence we can have another English sentence: "The office is next to the library."