Wood Mantel with Hidden Storage

Attach the two ends and the center divider to the bottom board with glue and 1-1/4" brad nails. Orient the grain of the ends so it runs horizontal — this is a small detail but it reads noticeably more finished than end-grain showing vertically.

Install the concealed surface-mount hinges and mount the front so it's flush on the bottom and sides — do this before the top goes on, while you can still reach inside easily. Test the swing and adjust the hinge position until the fit is right; this gets much harder to do once the box is closed up and on the wall.

Attach the top board to the ends and center divider — do not attach it to the front door, which needs to swing independently.

Measure and cut the 1x3 cleats to fit inside the box, then nail and glue them in place. Hang the mantel to wall studs using the 2-1/2" screws, checking with a level as you go — a mantel that isn't dead level is one of the more obvious mistakes on a piece this visible in a room.