Holding theAlt key, click (and hold) your mouse on an object.
Move the mouse left or right to orbit around the object.
Move the mouse up or down to pan in or out.

Holding theAlt+Ctrl keys, click (and hold) your mouse on an object.
Moving the mouse left or right still orbits around the object
but moving up or down now rotates over or under.

Press theEsckey to return the camera to its
original position and rotation!

Try looking on top of the upper block.

Have you seen all four signs?
If so, that's it!