How to insulate and build a decorative firebox in an unused fireplace?

[AdrianeS]

It's a total disaster. Basically just an empty hole in the wall with no insulation. The hole was previously covered by something resembling a very thick drywall which was formed to seal around the top and edges but this piece is very old and crumbling apart. I'm kind of at a loss for what to do here. Aside from lining the back wall with insulation, how can I go about building a decorative firebox? We won't actually be burning anything in it. I'd just like to seal it up to prevent drafts and make it look nicer than this!

 

[havasu]

I once covered a brick fireplace chimney top with a sheet metal covering, then caulked it in place.
What you do on the inside is up to you.

 

[Whatmeworry]

This is going to be one of those places where personal choice is big! I have a fireplace but building a fire in Texas just seems pretty silly, so we wanted to seal it for insulation. It was just a gale blowing through the room, even with the damper closed!

We went simple with cutting foam board like pink or blue board and wrapped it with black fabric to pin to the foam in the backside. With our fireplace there is a nice inset lip where we can stuff the fabric covered foam tight enough that it stays without attachments.
We have a TV too big for any spare space, so we now have it setting in front of the fireplace and most folks never notice we even have the fireplace! Mostly it is just the TV but if you peek behind then you can see black as if looking into a fireplace hole?
If artsy/crafty, one could change the cover look in any way you like, even seasonal for Christmas?
If doing this, I recommend adding a tab to pull at the top to get the stopper out when you want it.