To help us during the game I am trying to make a list of both locations' special characteristics, thus - I'm hopeing you could add/correct stuff:
Heroes can’t heal there, but can rest.
The maximum Influence in extension of the SS is the number marked on the SS’s tower.
They are always perilous.
Influence cannot be discarded from them, ever.
Anything else I'm missing?
You can always rest & heal there, even when certain abilities would prohibit it (such as the Witch-king's).*
Are never perilous (even if certain abilities would normally have them become perilous - like Gothmog's).*
There can never, ever, be Influence tokens there (even with special cards).
Monsters can't be in there (in the location), nor move there.
Only if the Hero wants would an Ambush occur there.
*this I'm not certain.