The founding legend is specific enough to feel credible. Yoritomo was consolidating his military government in Kamakura when the vision came, and the timing -- the triple serpent alignment of snake day, snake month, snake year -- gave the story a mathematical neatness that elevated it beyond ordinary dream narratives. The spirit Ugafukujin was a traditional Shinto kami of waters and harvest, but the shrine that Yoritomo established was never purely Shinto. From its inception, Zeniarai Benzaiten blended native kami worship with the Buddhist goddess Benzaiten -- the Japanese incarnation of the Hindu deity Sarasvati, goddess of everything that flows: water, music, eloquence, wealth. The shrine's shintai, the sacred object housing the kami, is a stone sculpture of a snake with a human head -- Ugafukujin rendered in physical form. This fusion of Shinto and Buddhism survived even the Meiji government's 1868 decree forcing the two religions apart. The shrine was absorbed into a larger shrine system for a time but became independent again in 1970 under its present name.

Yoritomo built the shrine, but the money-washing tradition did not begin until 1257, when Hojo Tokiyori -- the regent who effectively ruled Japan from Kamakura -- came to worship at the spring. Tokiyori washed his own coins in the cave waters and told the faithful to do the same, promising that Ugafukujin would multiply their money and grant prosperity to their descendants. The recommendation caught on. Over the following centuries, the practice evolved from a regent's endorsement into a deep-rooted folk belief that persists with genuine conviction today. Visitors purchase small wicker baskets at the shrine, place their money inside, and ladle the cold spring water over their currency. Some wash bills; some wash coins. The truly committed wash credit cards. The convention holds that the washed money should be spent, not hoarded -- circulating it is what activates the blessing. Whether or not anyone's fortune has literally doubled, the shrine has never lacked for visitors willing to test the theory.

Reaching Zeniarai Benzaiten requires a short walk through Kamakura's wooded western hills, climbing past residential streets that thin out into forest. The shrine is tucked into a narrow valley called Kakurezato -- 'hidden village' -- and the name is apt. The main entrance today is a tunnel bored through the rock face in 1958, its mouth framed by torii gates and its interior lit by bare bulbs. The tunnel deposits visitors directly into the shrine precinct, a compact space hemmed in by cliff walls on all sides, with the money-washing cave at its heart. The shrine's original entrance lies on the opposite side, near a cluster of tea houses, approached through a narrow path lined with more torii donated by the faithful. In the past, that winding path was the only way in, which explains why the area earned the name Kakurezato. The effect of either approach is the same: a sudden transition from ordinary neighborhood to enclosed sacred space, as if stepping behind a curtain in the hillside.

Zeniarai Benzaiten stands as one of Japan's clearest surviving examples of shinbutsu shugo -- the fusion of Shinto and Buddhism that characterized Japanese religion for over a thousand years before the Meiji separation. The shrine's dual identity is encoded in its very name: Ugafuku is the Shinto kami; Benzaiten is the Buddhist goddess. Both are associated with water, with serpents, with prosperity. The overlap was not accidental but theological -- under the honji suijaku framework, kami and buddhas were understood as different faces of the same spiritual reality. Archaeological excavations above the shrine's tunnel entrance uncovered several Buddhist steles, now housed in the Kamakura Museum of National Treasures, physical evidence of the centuries when praying at this spring meant addressing both traditions simultaneously. Most Japanese shrines were scrubbed of their Buddhist elements after 1868. Zeniarai Benzaiten kept its dual name and its dual character. The snake-headed stone still sits inside. The spring still flows through the cave. And tourists still wash their ten-thousand-yen notes, hedging their bets across every available deity.