...when clearly, all you need is a box?  Several months ago, I re-purposed a memory chest into a toy box for Vivi.  She's quite liked it (well, she mostly likes digging things out of it and making a mess, but there you are).  This evening, however, Vivi re-purposed the box herself.  
Yes, that's right.  She climbed inside of it.  
A castle?  A pirate ship?  A rocket?  Who knows what form the box took in our little lady's mind?  
Her activities did not necessarily lend a clue.  We found her...
Throwing a ball from the box.
Enjoying a tasty snack in the box.
At any rate.  She was having a great time!  Who knows what was going on in her head, but she was very, very happy to find out she fits in her toybox.
 

