Why is the Secret Door Secret?

One way we could add details and logic to secret doors is to look at them from the angle of what was meant to be hidden.  I broke that down into four categories.  Here are some ideas on each:

Individuals hiding something from society
Probably more crudely built in easy-to-work materials since one person was doing it.  These might be more covered holes or dirt tunnels than true secret corridors.  Or they could be one of the other types of passages that have been forgotten by everyone, now found by this individual and re-purposed.

The peeper will have holes into the most private areas of the community and maybe a network of these.  The hoarder has a pantry hidden away with alcohol, preserved foods, anything the community is only allowed certain amounts of.  That and the Shirker's quiet hideaway could be nice finds for visiting adventurers.  Mania is where your celebrity stalker pastes up their pictures or the miniatures collector stores their armies.  Blasphemy is where dark idols are kept.  But, really, depending on the community anything considered forbidden could be reason to hide here.

Small groups hiding from society
Trysts allow for forbidden love and will usually span long distances, literally or culturally.  So the Montagues live far from the Capulets, or the king sneaks right next door into the maid's quarters.  These lover's passages should probably have secret doors on each end.  The rest in this category are the cults and secret societies.  These will be better built with warning bells and even traps.  They should lead to, not just more windy little passages, but hidden rooms, big enough for people to meet and scheme.  Could include small barracks, warehouses, or libraries.  Forbidden lore could include magics or heretical religious teachings.

Rulers hiding from society
These are the best quality, built with money, planning, and plenty of labor.  Probably have locks.  The peepholes will be not just into bedrooms, but places people might meet and talk.  Some passages could open into travel routes for easy disappearing of troublesome folks.  Fraud includes the hidden panels that allow priests to make an idol "eat" its offerings.

Society hiding from invaders
These are of similar quality to those built by the rulers, unless they are built after occupation and then they'll be more like the individual's crude attempts but full of traps.  Peepholes may function as murder holes.  The escape route may be one-way and much larger than the ruler's bolthole.  The flanking and guerrilla type should be located in tactically advantageous positions.  Most people in the community should know about these.

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I have been messing about with this for several days trying to figure out the best way to present it.  I had an idea that you might use little icons in the table-- eyes, bells, and such-- to represent the features each category has..  But I figure I'll just post it now to share the ideas and revise it later.