An illuminated glass block Christmas decoration is one with lights placed inside the glass block. Drill a hole in the back of the glass block and feed Christmas lights into the block until only the plug and a short length of cord remain outside the glass block. Any kind of small, holiday lights can be placed inside the glass block. You can use colored lights or white lights. Once your lights are inside the glass block, add Christmas decals to the exterior, an activity appropriate for children. Supervise closely so the glass block doesn't get knocked down as your child applies the decals.