The Seizansō (西山荘), also known as the Nishiyama Goten (西山御殿) was the retirement villa of Tokugawa Mitsukuni, the second daimyō of Mito Domain under the Edo Period Tokugawa shogunate of Japan.

[1] The Seizansō villa was constructed in 1690, and was the residence of Tokugawa Mitsukuni from 1691 unto his death in 1700.

The villa burned down in 1817, but was rebuilt in 1819 by the 8th daimyō of Mito Domain, Tokugawa Narinobu.

The interior has rough walls, which reflects Tokugawa Mitsukuni's dislike for any form of ostentation.

Outside the main structure is a smaller samurai residence for use by his guards and a Japanese garden.