Why did Paul go to Greece instead of going to Bithynia?

Les explains that Paul originally intended to go to Bithynia, located along the Black Sea, and from there go back down through Asia. Instead, the Holy Spirit led him across to Greece. The cities that come later in the book of Acts include going from Troas to Philippi, then Thessalonica, down to Berea, down to Athens, over to Corinth, and then back to Antioch. On another trip he would retrace all this. Later, in his prison experience, he left Caesarea, touched Cyprus, encountered a storm, was tossed to and fro, ended up at the little island of Melita, then went up the coast and finally reached Rome in the closing part of Acts.