There are many ways to hide a flat TV in a plain sight. Although this DIY solution is probably the coolest one I’ve seen so far. It’s especially perfect if your TV is mounted above the fireplace. The idea is to cover the TV with an artwork on two panels on a sliding closet door track.
To get the height of your panels measure from the mantel to your ceiling, then subtract 2″. The width of your panels should be the width of your TV plus 2″. The track should be long enough to accomodate two such panels (at least double the sum of their widths). The determine how far out from the wall the track should be installed measure the depth of your TV and its wall-mount bracket plus an inch. When you know all these things install the track and attach the slider hardware to your panels to put them on this track. Next, paint your panels, install them and enjoy your work!