Pietro Micca is an Italian heroic figure. He was a soldier in one of the many wars against France back in the 1700s & 1800s. In these wars, the French were outside the city and had Turin under siege with cannons. Someone in the Italian army came up with idea of digging tunnels out from the city to underneath where the French cannons were. Soldiers would dig the tunnels, and would locate the French cannons by watching beans bounce (when the beans bounced straight up when a cannon fired versus moving right or left, they knew they were underneath a cannon).
Once the cannons were located, the soldiers would set explosives at the end of the tunnel, run a fuse as far as they could and then light it. If the tunnel was dug correctly, the explosion would shoot straight upward and take out the French cannon above. This was in theory. In practice, this was very dangerous work. If the tunnel was dug too shallow, the ground would cave in under the weight of the armies above. Often, the explosion would shoot back down the tunnel, rather than straight up, and would kill the soldiers before they could get safely out of the way.
Pietro Micca was one of the soldiers in charge of the tunnels. I can't remember the whole story, but basically, he saved many lives when the French discovered the tunnels by lighting explosions in the tunnels as the French were invading them. He was killed in the process, but his actions stopped the French and gave Piedmont the victory.
In the museum, a guide takes you down under the city into some of the actual tunnels that were used during the war. Many of the tunnels have been excavated, and it is believed the spot has been found where Pietra Micca actually died. This is a very interesting slice of history, and it's quite an experience to be under the city. Bring a jacket, as the tunnels are cool. Even if it's 90+ degrees outside, the tunnels are around 60 degrees. Ask for an English speaking guide, so you can hear the story for yourself.