Shireya collects gotochi postcard, and I sent her the Mie 2014 issue, featuring the ninja and Iga Ueno Castle.
Iga (伊賀) is a famous ninja village in Mie Prefecture (三重県). Ninja is a covert agent or mercenary well-trained in assassination, collection of information, poisoning etc. They wrote in their own language to avoid leakage of information. You can see on the postcard (below the word "MIE").
In normal days, ninja did not dress as shown on the postcard. On the other hand, they dressed as if a monk or a farmer, presenting themselves as a normal person to avoid suspecion.
The ninja on the left is holding a shuriken (手裏剣, or "sword on hand"). It was usually poisoned.
Behind the ninja is Iga Ueno Castle (伊賀上野城). It was built by Toudou Takatora (藤堂高虎), a daimyo in the 15th to 16th century. He was bestowed the state of Iga after the Battle of Sekigahara. As a skilled castle-builder, Toudou reconstructed the castle. A 29m wall was added for better defence.
In return, I got a nice card of Crete from Shireya. She bought the card when she was travelling there.