On July 6, 1942 Anne Frank's family moved into a hidden apartment in the large building where Otto Frank worked. The following clip reveals what the Secret Annex looked like.
So there's a glimpse.
But if you want a more leisurely view, one in which you choose which room to visit and how long to stay, one with fascinating narration about the occupants and their relationships, I recommend the virtual 3-D tour of the Secret Annex.
After following the link above, click on the bookcase and watch it swing open. Enter the Secret Annex and imagine being in this space for over 2 years.
Imagine that even looking out the window was a dangerous activity.