I always liked the sound of you. I know you're another word for a valley (or "river valley"), but it's nice to have multiple words to describe the same or similar landscapes, and I am going to use you to make my point today, which is that the landscape in a story is such an important part of the tale.
Every story has a unique environment. Maybe somewhere on Earth, or an alternate Earth, or a fantasy world or planet. Whether it's a place we know on Earth or a fantastical world, the setting has to feel real in the book, to us, our characters, and our readers. Whatever your setting, it can aid or hinder your characters. Do they have a city as their playground? Mountains? Vales? Meadows, forests, volcanoes, deserts, rainforests, vast snowy plains? What is the weather like in your characters' environment? Do they live in the Old West in the United States? Victorian England? Ancient Rome? Modern day Japan? Do they live underground? In a floating city? On a spaceship? Do they have a lot of space or hardly any at all?
It's fun to explore the places your character lives or travels through a book, and it's important to the world-building and to deciding what your character is going to face.
*Tell me about your landscapes! What kind of environment do you have your characters in? Do you find that it adds to the challenges or aids your characters along their journeys?