If you live in a valley, you probably get more fog than they do up in the hills around you. Fog tends to be more common down in the valley, the low area that often forms near a river.
If you're into fishing, swimming, and tubing, then a valley is the place for you, because valleys usually have rivers or other streams running through them. The Napa Valley is an area in northern California that is famous for its good wine and food, though technically it's not all a valley; parts of it are quite hilly. Another famous valley, the San Fernando, lies at the foot of the hills of Los Angeles. You might have heard of the infamous "Valley Girl." In movies, Valley girls are usually blonde and say "like" and "totally" a lot. "Like, oh, my God! That low, flat stretch of terrain, is like, totally a valley!"