What To Do With A Square “Hole?” Opinions, Please

To make a long story fairly short we're getting used cabinets from my mother in-law (if they fit on our wall) for free but in order to put them up on the wall we needed to and still need to do a bit of prep work. Even if the cabinets don't fit, the paneling had to go, so either way it's work that needs to be done.

We or should I say, my wife Lynn and Dylan took down this awful looking paneling that wasn't put properly up to begin with. If we're going to have cabinets put up above the fridge and stove then the wall needs be flat without loosely installed paneling. After everyone wakes up we need to sand the joint compound flat and paint. The kitchen wall will be a "shortbread" yellow when it's all done.

My question is about what to do with the hole that we discovered after the paneling came down. We knew it was there to a degree because of the other side but paid no attention to it as the kitchen side was covered with paneling.

Should we put a stained plexiglass pane in there? That was one idea. Should we put in a small fan circulation? How about an unbreakable nick nack? Then there is this idea, maybe we should leave the boxy hole as a perch for the cats? Opinions, please.