ON ARRIVAL, I was guided by a man dressed in black through a concealed door in the wall to a narrow path on the other side.
After passing a "waterfall for training ninja", I stopped to put my hands together in a ninja pose. When I said "Nin!", a drawbridge appeared and I found myself in a space that appeared to be a legendary land hidden from human eyes.
Welcome to Ninja Akasaka, a theme restaurant in the Akasaka district of Tokyo.
The dramatic way the guests are received and its entertaining menu make the restaurant popular among foreign visitors.
Ninja warriors are known across the world as exotic Japanese heroes widely depicted in anime and films.
Last year, nearly 20 million people visited Japan.
Many wanted to see ninja and some Japanese businesses are catering to their desire.
The Akasaka restaurant has 27 private rooms, each modelled after a stone house.
The menu, in the form of a hand scroll recording secret ninja techniques, includes ninja-themed dishes.
There are crackers in the shape of shuriken throwing stars, a weapon commonly associated with ninja fighters; and turban shells with lids that are blown away when a fuse is lit.
While eating, diners are entertained by a magic show performed by a magician dressed as a high-ranking ninja.
The restaurant, opened in 2001, has been introduced in many guidebooks and on TV programmes overseas.
About 40 per cent of customers are foreign tourists - more than 20,000 each year.
"I heard about this restaurant from a friend of my wife," said a man in his late 50s who came from Switzerland with two family members. "My daughter is thrilled to be here because she likes ninja."
Some foreigners want to buy ninja-related souvenirs.
Shinobiya Asakusa Ekimise is one such store established to serve them. It opened in 2012 in a building near Kaminarimon gate in Asakusa, Taito Ward, Tokyo.
It sells over 3,000 items, such as shuriken and makibishi caltrops (ground spikes) made from rubber or iron, model swords and ninja outfits.
It also sells items that ninja fighters historically never used, such as sai and nunchaku - traditional weapons used in Okinawan martial arts.
According to the store manager Toru Oyagi, sai and nunchaku are considered to be ninja weapons overseas as they are used in the United States animated series Teenage Mutant Ninja Turtles.
"They are here because people want them," Mr Oyagi said.
At the store, visitors are given a chance to throw an iron shuriken at a target 2m away.
One female Italian tourist had a hard time getting the shuriken to stick in the target after he instructed her on how to throw the weapon. "It's difficult for me," she said.
Visitors can look forward to more ninja-related highlights during their next trip to Japan.
On Oct 9 last year, governors and mayors of prefectures and cities associated with ninja came together in Tokyo to inaugurate the Japan Ninja Council to look into tourism and regional vitalisation through ninja.
The prefectures are Mie, Shiga, Kanagawa and Saga, which are associated with ninja schools such as Iga, Koka and Fuma. The governors and mayors attended the inauguration wearing ninja outfits.
There is even a government project for training animators in the works.
A story titled Colourful Ninja Iromaki is now being produced after being selected by Animetamago 2016, a project for training young talented animators, sponsored by the Cultural Affairs Agency.
In the story, Himeno, a third-grade primary school girl, moves to the countryside, where she meets three ninja.
Each ninja has a special technique and a signature colour, and each has multiple alter egos. Like colours of paint, when alter egos blend, new ninja emerge, producing different signature colours and techniques. The ninja team up to save Himeno and her family from a crisis.
"We'll make ninja brands and promote the ninja boom," said the governor of Mie, Eikei Suzuki, the first chairman of the Japan Ninja Council.