Geographically, a valley is an area of lower altitude with mountains or hills on either side.
Evolutionists, who require a belief in an Old Earth, claim that a river formed the Grand Canyon over thousands of years. But the shape of the Canyon proves otherwise. Similar claims that glaciers formed valleys should be carefully scrutinized compared to the more plausible explanation of the valleys having been formed by a flood.
Metaphorically, a valley is a time when a soul is going through tribulation, turmoil, depression or just a really bad day.