Ryujo Park is in Otawara, Tochigi Prefecture.

Here, "Ryujo" is written "龍城".

The reason why Ryuujou is wearing Amagi's clothes is that it's really just a visual pun. "龍城" can be constructed as a portmanteau of "龍驤" and "天城". "龍城" and "龍驤" are also pronounced the same.