Seikai Kunii founded the Seishinsha, a group that studies modern calligraphy, in 1917 and this museum features his calligraphy, calligraphy he has collected, and special exhibits along with information about modern calligraphy (in Japanese).
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山形市郷土館
Built in 1876 as a hospital, it's known for its unique architecture. It was registered as an Important Cultural Property in 1966. The exhibits show the building's history and information about medical studies during that time period.
山形県立博物館
A museum with exhibits of historic artifacts from Yamagata Prefecture. It is home to the famous "Jomon Goddess" (Jomon no Megami), a ceramic statue of a goddess forged in the Jomon Period. For Japanese history buffs, it's worth a visit just to see this object. The prefecture's famous pilgrimage shrines (the Dewa Sanzan) and temple (Yamadera) also have informative exhibits. In addition to the historical exhibits, the museum also has displays on the local culture, rocks and minerals, and flora and fauna.
山形城
The original castle was constructed in 1357 by Kaneyori Mogami but the castle was greatly expanded by Yoshiaki Mogami nearly 200 years later. The castle contained a palace building and other structures protected by multiple walled sections with turrets surrounded by a moat. It was the largest castle in the Tohoku region, but it never had a donjon. Yoshiaki also built up the surrounding area as a respectable castle town, both expanding it and improving the existing infrastructure. He is sometimes called the "founder" of Yamagata City, even though people had been living there long before his lifetime. None of the original structures survive today however, efforts are ongoing to rebuild each part of the former castle. Reconstructions have been made out of wood to stay true to the original castle. You can wander the castle grounds and enter the Ninomaru East Gate building to learn a bit more about the castle. The JR Ou Main Line travels directly along the moat past the Ninomaru Gate. It's fun for trainspotters to get pictures of the trains with the castle but the downside is that it limits the angles from which you can view it. The site is listed as one of the top 100 castles in Japan.
山形美術館 yamagata bijutsukan
The museum's permanent collection contains works by Kichiro Hasegawa, Matsuo Basho, and Claude Monet. Special exhibits typically show for about a month at a time, so check the museum website to see what will be featured during your visit.
最上義光歴史館
Mogami Yoshiaki was a daimyo of the Dewa Province. He is credited for vastly expanding Yamagata Castle and transforming the area from a modest, somewhat run-down town into a respectable modern city. He fought many battles in the region and gained territory for siding with the Tokugawa during the Battle of Sekigahara to make his domain one of the top in the nation at the time. The museum includes exhibits about the city's history in addition to those about Mogami.
やまがた伝統こけし館 yamagata dentō kokeshikan
The Kokeshikan has displays of old kokeshi and explanations of the various types of kokeshi. Visitors can also try painting their own kokeshi dolls.