"Five times at the hands of the Jews I received forty lashes less one: (40 lashes was a death penalty) three times I was beaten with rods: I was stoned once, shipwrecked three times; I passed a day and a night on the sea. I travelled continually, endangered by floods, robbers, my own people, the Gentiles; imperiled in the city, in the desert, at sea, by false brothers; enduring labor, hardship, many sleepless nights; in hunger and thirst and frequent fastings; in cold and nakedness." 2 Corinthinns 11: 24-27
Paul's three missionary journeys of service through the Mediterranean took in the following towns and cities, and probably more. Then followed the journey to Rome, which he had hoped to make as a free man. But when the journey came at last, Paul was under guard, as a prisoner of Caesar.
German researcher Heinz Warnecke has suggested that the shipwreck on the way to Rome took place bot on Malta but on Cephalonia - and his reasoning is interesting. See This Article - worth reading. HOWEVER, some of his arguments - eg the nature of the inhabitants, do not seem to square with what Acts says.
It is also thought that Paul may have travelled to Spain and even Britain in the 6 missing years between his time of house arrest and later imprisonment in Rome.
This is not pure speculation, since Paul himself said he was keen to go to Spain. Also there was a strong trade in tin with Britain, carried on in Jesus' day by Joseph of Arimathea.
There are passages in the writings of Clement, Eusebius, Chrysostom, and Jerome to the effect that Paul had preached the gospel in the East and in the West of the Empire. Clement states that he had gone to 'the extremity of the West' before his martyrdom. [The Search for the Twelve Apostles - William Steuart McBirnie.]