If a place is seedy, it is dirty, not safe, and maybe a little scary.
The word seedy makes people think of bad places, maybe with bad people.
Examples:
The seedy alley was dark and dirty.
I don't want to go to the seedy part of town.
The seedy hotel was not a good place to stay.
The seedy restaurant had bugs in the food.
The seedy neighborhood was the scariest place I've ever seen.
The seedy bar was full of rough people.