Okay kiddo, so a national redoubt is kind of like a big hideout or shelter that a country might have in case something really bad happens, like a war or a natural disaster. It's a secret and safe place that people can go to for protection.
Switzerland, a country in Europe, has a national redoubt too. It's a big network of tunnels, bunkers, and other hidden places that the government made to keep people safe during a war. The government built this redoubt because they were worried that their country might be in danger during a war.
The national redoubt is designed to protect people from bombs and other dangerous things. There are emergency supplies like food, water, and medical equipment in the redoubt so people can survive for a long time. There are also many secret entrances and exits that are hard to find, so the enemy won't be able to find them either.
Even though the national redoubt is secret and not many people know about it, Switzerland still makes sure it's ready in case something happens. They have people who check on it regularly to make sure everything is working properly and ready to use. Luckily, they haven't had to use it yet, and let's hope they never have to!