Okay kiddo, so a "festung" is a German word that means "fortress" or "stronghold". It's like a really strong and sturdy building or place that is designed to protect people inside from things that might try to hurt them, like enemies or dangerous animals.
Imagine you're building a sandcastle at the beach and you want it to be really, really strong. You can make tall walls and dig a big trench around it to keep the water away. That's kind of like what a festung is, but much bigger and way more serious.
People might build a festung during a war to protect themselves and their families from enemy soldiers. They might also build a festung to protect important things like castles, cities, or even valuable treasure. The idea is to keep the bad guys out and keep the good guys safe inside.
Does that make sense, little one?