If anything, Gogos thought someone from a nearby country, maybe the Netherlands, would find it and reply.
But last Tuesday, she received a reply from the other side of the world: Auckland, New Zealand.
"I never thought it would go that far," she told ABC News in a telephone interview on Wednesday.
Gogos sent the original letter in 2012 or 2013 after receiving a glass bottle as a present. She thought at the time it looked exactly like a bottle you'd send out to sea with a letter in it.
She and her children, Silas and Maja, along with her friend's children, Frida and Jon, wrote: "Please send us a message when you find our message in a bottle."
Now she and her family are trying to find those who sent the response to their home in Bonn. It came with four names -- Scott, Julia, Lea and Alice Joy -- and a short message: "We found this message in a bottle and are sending it back from Auckland, New Zealand. It has traveled a long way! Take care."
Gogos said she was in disbelief.
"They really took the time to respond to our message in a bottle. … It really is, for us, exciting and it makes us happy," she said.
Her daughter, Maja, now 12, was so young when they sent the original message she'd since forgotten about it.
"I had to explain to her, 'Well, years ago, we threw a bottle into the Rhine River," Gogos said. "We had to check on a map where New Zealand is. They couldn't really imagine how far the bottle had traveled."
They hope to find the people in Auckland who sent the response to thank them. She also has a few questions, like what the bottle looked like when they found it and what they did with it.
"Did they keep it as a souvenir? Did they throw it away? Or maybe they started a new message in a bottle," Gogos wondered. "It would be cool to know."