The lowest levels are filled with horrible creatures, and Underground Zombies descended from tourists who got lost in the maze of passages. They feed on more recent lost tourists.
This middle area is almost as dangerous. There is basically no law down in these parts, so terrible people torment others.
This area is the top level. This is where most people are and is probably the safest. This specific scene is from the Battle of Courscant.
This is a birds eye view of the top layer. This scene takes place near the end of Episode III, and is the burning of the Jedi Temple. Off to the side is the senate building. A ship is flying through the sky.