This handmade oak wall shelf we found on Etsy has a secret drop down shelf hidden inside. The top shelf stays flat to keep from disturbing anything on display. The drop down compartment has a felt lined interior held closed by a magnet lock. To open you place a wooden barrel with a neodymium magnet near the latch.
This type of shelf is a convenient way to store medication or gun at easy reach, but out of plain sight and the hands of little ones.