Walls and Ceilings - removing AC unit, what to fill wall in with?

I have a thru the wall air conditioner mounted 1 ft from the top of my living room ceiling. It's been broken for years so i want to take it out. it's about 23 wide x 15 high. It opens out to my breezeway which is the same permastone as the rest of my house. I thought maybe i could get a small custom window in there but then thought it would look kind of silly and not really provide me with light etc. Then i thought just board it up and make it just a regular wall inside and as best as i could outside.

Then someone said why not do glass block? I'm looking for a doing it yourself project so this seemed like a good idea at what i hope would be a reasonable price.

But i was wondering if you had any other ideas that wouldnt cost a lot and would be doityourself?

They make a plastic "glass block" window that can be ordered in a custom size. You just slip the unit in and seal. Don't have a manufacturer's name handy but you can Google it.