Take a pic after all the halloween stuff is gone but it looks like you have some wood slat trim above the fP so for me I would look for a piece of art that would fit into the gap in the trim above the mantel .

There is no bottom piece for the molding trim above the mantel, and the ceiling is low, so this would be ideal for a leaning piece of art or mirror that sits on the mantel and fits proportionately within the molding. Secure it so it doesn't tip over. Alien Tape works wonders.

“I would look for a piece of art that would fit into the gap in the trim above the mantel.”

Agree, and you’d need little else on the mantel with the art.