An adult coloring book of castle towns across Japan, with pictures in postcard size. It is part of the Otona no Nurie Postcard Book series from Kawade Shobo Shinsha, and the pictures are by illustrator Tomohisa Monma.
The landscapes include Edo Castle, Matsushiro Castle in Nagano Prefecture and the old streets of Hagi in Yamaguchi Prefecture. The book is an A4-variant size with 40 pages.
Each picture is laid out as a postcard, so you can mail it after coloring. You can also visit the place in the picture and send the card from there.