He said: "There was more than one of them, and their behaviour was correct and polite, and they took good care of me and my requirements.
"I'm very happy to be home, as you can understand. As you can see I am well."
State television reported that one of the kidnappers told Panagopoulos: "Thanks very much, you're free to go grandpappy," before releasing him.
Panagopoulos, who said he was "still dazed," thanked the police and Greek and foreign politicians for supporting him.
He said his family had received messages of support from across the world.
The shipping magnate said: "I discovered that I have thousands, if not millions of friends in Greece and throughout the world.
"And, you know, that is a unique sensation... My family received many thousands of [supportive] messages."
His family are reported to have paid kidnappers a ransom of between $19m and $26m to secure his release.
While they did not confirm the amount, police said it was the largest ever known sum to have been paid in a Greek kidnap case.
Panagopoulos' wife, Katerina, said last week that she was "ready to pay the sum" to the abductors, appealing to them to release her husband, who needs daily medical treatment including insulin.
But Panagopoulos revealed that he had his medicine with him when he was abducted, and his captors ensured he received it.
Police are hoping that a shipment of medication, which has been traced to a pharmacy north of Athens, may help them locate the kidnappers.
The millionaire and his driver were abducted on January 12 when three armed men blocked his car, shortly after he had left his home.
The driver was found later tied to a tree with handcuffs and a hood placed over his head, police said.
Panagopoulos, one of Greece's richest men, founded Royal Cruise Line in 1971.
After selling the company, he founded Attica Group, which owns two of Greece's largest ferry lines.
Kidnappings, which are usually rare in Greece, have made headlines in the past year with the abductions of two other prominent figures.
In December, Epameinondas Gerasimopoulos, a cardiologist, was taken by gunmen from his home in Vari, a suburb of Athens, and is still missing.
In June, George Mylonas, a leading industrialist, was snatched from outside his home in Thessaloniki in northern Greece.
He was released two weeks later after his family paid a ransom.