Am I lacking some common knowledge here? I expected some plans and explanations of the circumstances that lead to this specific piece of property staying hidden

Am I lacking some common knowledge here? I expected some plans and explanations of the circumstances that lead to this specific piece of property staying hidden for so long. Was it an abandoned wing? Where's the entry? Was the door hidden or disguised in some way? TFA has only photos of the inside and lots of $ numbers. Pretty disappointing.