British Border officials seized €26,000 stuffed inside the bra of a Romanian woman as she arrived in Holyhead on a ferry from Ireland.
The cash was discovered during checks at the North Wales port, the UK Border Agency said.
The woman, travelling from Dublin, claimed she earned the money from the sale of a business in Ireland.
But she could provide no proof of having sold a business or give any further explanation for how she came to be carrying the proceeds from the alleged sale in cash.
She also could not explain why she had concealed such a large sum of cash, which was in €500 notes, the agency added.
Earlier this month, the Britian's Serious Organised Crime Agency (Soca) announced that the €500 note would no longer be available over the counter in the UK.
That decision was made after evidence showed more than 90pc of UK demand for the large denomination note was linked to criminality.
Bob Lyne, UK Border Agency Assistant Director for Wales, said: "UK Border Agency officers are working hard at all our ports to prevent drugs, contraband or the potential proceeds of crime from entering or leaving the UK.
"Where we suspect that cash may be linked with criminal activity, we have the power to seize it and it will only be handed back if it is later proved to be legitimate."
The money found on the Romanian woman travelling from Ireland was seized under the UK Proceeds of Crime Act at Holyhead on May 18.
The woman was told that it would only be returned to her if she could provide proof to a court that the money came from a legitimate source.
So far, she has not been able to do so.