More about Vi Hart,, Flatlands and Mobius strips- here: http://www.brainpickings.org/index.php/2011/01/20/vi-hart-flatland-on-a-mobius-strip/

If you haven't read the book Flatlands - here is something similar - - but the Flatlands book implies a possibility of the fourth dimension. I, personally, do not care much for this video.

Finally - here is a TED talks on dimensions:

Activity:

Building in 3D Activity:

OK- if you got this far, here is one more: