Saikan is a Shinto pilgrim lodge & lunch restaurant inside a former Buddhist temple called Shôon'in built in 1697. Following the religious separation between Shinto and Buddhism in 1868 (1869 in Haguro), the building was converted to Shintoism and had its name changed for Saikan.
Saikan is an obligatory step for the Shinto yamabushi during their retreat training. For example, it is where the yamabushi closes the Shoreisai ceremony by eating the Nishi sushi.
Every day, Chef Ito Shinkichi serves his version of the Dewa Sanzan shojin-ryori: a Shinto version of the originally Buddhist dish that aims to pay tribute to the greatness of nature.
The shojin-ryori can be made vegan, but you need to warn the chef that you are vegan 3 days in advance.