Fireplace Into Book Nook: A Plan

Our house was built in the 50's and at some point, someone added on a room to the back.  It's nice because it adds onto our square footage, but other than that, I feel like this room is pointless.  Whoever added it on did it with some mysterious purpose in mind that I haven't been able to figure out (pool table?) and every time I try to figure out how to use it, I run up against problems.

The placement of the doors and windows, plus the fact that there are several built in cabinets, makes it impossible to put furniture in it.  There's room for a couch against one wall ... and other than that, everything else has to be in the middle of the room.  Irritating.  The wall outlets are in stupid places, the light switches don't go to anything, and then there is the fireplace.  The stupid, stupid fireplace.

We've built a fire in it exactly once, because it's hot where we live and fireplace worthy days that fall on a weekend are truly once-a-year things.  The rest of the time, it just sits there, unused, and because whoever added it to the house was a jerk, it takes up an entire corner.  As for why the hearth juts out to the left halfway along the wall, making further unusable space, I have no answers.

Last weekend, we converted it (or finished converting it) into a play room.  There's nothing else to be done with it.  We moved a few toys in, including the beloved train table, and added a bookcase.  Note that the bookcase has to go in front of a built-in because there's no other place to put it.  That cabinet is full of Christmas stuff, so we don't need to access it all that often.

I want to turn to fireplace into a reading nook.  Or, a nook for any purpose, really.  Anything will be better than a fireplace.  First I'll have to figure out how to remove the screen, and then deal with how filthy it is.  I would love to tack up some fabric and be done, but I'm not sure how a person attaches fabric to bricks.  I welcome any and all ideas on how to figure this out.