Kai Struve, 23, was tearing out old bathroom fixtures in the Moosach district flat when he found the sack of cash in the tub casing.
“The honest young man let police know directly,” the authorities said in a statement.
Police investigation found that the large sum belonged to the apartment's former tenant, an 88-year-old who now lives in a retirement home.
“Apparently the pensioner forgot the bunch of money in his apartment due to his dementia,” the statement continued.
The sum is currently at the Bavarian city's guardianship court, meanwhile Druve will receive a €3,000 reward.
German law dictates that those who return found items worth more than €500 are entitled to €25 plus three percent of the item's additional worth.