The surroundings or environment in which a person lives or operates.
The word milieu makes people think of the place where someone is, and how that place affects them.
Examples:
The city was his milieu.
She felt comfortable in that milieu.
The countryside is a good milieu for animals.
The school was a good milieu for learning.
The ocean is a great milieu for fish.
The forest was a dangerous milieu for the lost hiker.