This is a simple story related achievement. and penultimate one you'll earn in the game. All you need to do is assemble the broken mirror in the kitchen of the bunker.
1. Shard of glass is on the kitchen counter next to the sink.
2. There is a shard in the bathroom on the floor to the right as soon as you enter the room.
3. There is a shard in the final "office"
Arrange them in the broken mirror in their correct placement based on shape, and the achievement will pop.