Like a grim eagle upon it's nest, the great black block of Tannia Castle looks down upon the city of the same name. Despite the fact that some of those brought within it's walls never come out again, the castle is still looked upon well by most of the city's inhabitants, a place of protection rather then a place of terror.
The spirit of a creature trapped in amber cannot escape to it’s afterlife / next incarnation / whatever.
Such trapped spirits can be contacted by those who know the right rituals and magical power derived from them – typically the power to control one individual of that species.
Can by quite powerful if the creature is a colony insect (ant, bee, wasp, etc) – simply control the queen and you command the whole colony.