A letter written to a 12-year old girl in Lithuania was delivered in December, almost 51 years after it was sent by a pen pal in Poland.
"I thought that someone was pranking me," said Genovefa Klonovska after being handed the letter, which included a handmade coloured rose and two paper dolls.
The letter, and 17 others, dirty and crumpled, fell out of a ventilation hole this summer as a wall was demolished in a former post office on the outskirts of Vilnius.
"The workers suggested we throw the old letters away but I called the post office instead," said Jurgis Vilutis, the owner of the building. "I'm so happy they got interested."
The letters, from the late 1960s and early 1970s, were probably hidden by an unscrupulous postal worker after he searched them for cash or valuables, Mr Vilutis said.
Lithuania was part of the Soviet Union then, and the senders were emigrant relatives or pen pals from places such as Australia, Poland and Russia.
Street names and their numbering have changed in Vilnius, and post office workers spent months looking for the right houses and talking to current tenants and neighbours, tracking down the recipients' addresses.
Only five were found. In several cases, children of dead recipients were handed a lost letter.
"We felt a moral duty to do this," said Deimante Zebrauskaite, head of the customer experience department at Lithuania Post.
"One lady compared the experience to receiving a message from a bottle thrown into sea. People were emotional. Some felt they saw a part of daily life of their deceased parents."
In the letter to Ms Klonovska, sent from Koczary in Poland and stamped in 1970, a girl named Ewa complains that buses no longer reach her village, so she has to walk in minus 23°C cold. Ewa also asks for pictures of actors.
Now in her 60s, Ms Klonovska has no memory of Ewa. She probably wrote to her after finding her address in newspaper advertisements for pen pals, and the relationship stopped after the letter was not delivered.
"So good that the letter was inconsequential. The loss was not life-changing," said Ms Klonovska. "What if they delivered a lost letter from a suitor to his love, and their wedding never happened?"
