The Street View feature of Google Maps lets you move around the streets of these cities using the mouse but for a more smooth walking experience, try the following keyboard shortcuts (some are undocumented):
*you may practice these key combination here itself on the Street view map embedded above. Just make sure you click the map once before using these keys.
a (or left arrow key) - rotate 45 degrees in counter-clockwise direction.
d (or right arrow key) - rotate 45 degrees in clockwise direction.
w (or PageUp key) - look up towards the sky.
s (or PageDown key) - look down towards the road.
+ (plus key) - zoom in for a close-up view.
- (minus key) - zoom out one level.
The up and down arrow keys help you navigate the streets in forward and backward directions but make sure that the zoom level is set to none else these arrow keys will make you look up or down.
Another update: The Google Maps picture that recorded a police arrest has now been deleted from Street View. That was quick.