The exact location of the valley is unknown.
Climate and Area
Hell's Valley is avast bleak wasteland that leaks unknown poisonous gas. According to Precht, Hell's Valley was the center of an old extinct civilization where people used to worship flowers and plants, until the climate change destroyed everything.
During Yuri Dreyar, Warrod Sequen and Precht Gaebolg search for Wild Rainbow, they went across the valley and entered the ancient ruins in it. After surviving the various snare, they come across an inside cave where they fight the said plant Magic beast. After defeating it, the three treasure hunters departs from the valley with their booty.