You are considering a vintage Czechoslovakian Bakelite PP Mi-D Mine. These were copies of the infamous Schu-Mine designed by Nazi Germany in World War II. Like the original wood box mine, this was created using bakelite to avoid metal detection. A detonator with pins would stick out the side of the box, and with sufficient pressure (like a footstep), it would detonate. You could also use these in a trip-wire fashion. This example does not include its inert detonator.