長野県諏訪市にあるお城です．
かつては諏訪湖に突き出した水城で「諏訪の浮城（すわのうきしろ）」と呼ばれていたが、江戸時代初めに諏訪湖の干拓が行われ、水城の面影は失われました．
しかし、浮城の異名を持っていたことから日本三大湖城の一つに数えられています．
2017年（平成29年）4月6日に、続日本100名城（130番）に選定されました．
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This castle is located in Suwa City, Nagano Prefecture.
It was once called "Suwa no Ukishiro" (Suwa floating castle) because of its location on Suwa Lake, but the lake was reclaimed at the beginning of the Edo period and the water castle was lost.
However, it is considered one of the three major lake castles in Japan because of its nickname of "floating castle.
On April 6, 2017 (Heisei 29), it was selected as one of the 100 best castles in Japan (No. 130).