Zao-san (Mount Zao) is a volcano on the border of Yamagata and Miyagi prefectures about a 45-minute drive southeast of Yamagata city. It is a popular ski destination, but it is also a pleasant summer/fall getaway. The main attraction is a teal-hued crater lake called Goshikinuma or simply "Okama (bowl)", where you can walk around and take in the spectacular scenery of the surrounding mountains. There are also dozens of makeshift shrines or markers constructed form pebbles and stones as well as a traditional subdued Shinto shrine with a stately wooden torii (gate).
More info
Find out more about Mount Zao.