Greece is famous for the islands but the main land is also very beautiful! You can visit historic places like Vergina or Ancient Olympia, stay under the astonishing god shaped rocks at Meteora, feel a part of ancient history while getting an oracle from Delphi or sightseeing Ancient Athens.
Cycling has become familiar to greeks over the last years, and the infrastructure gets better day by day so more people may enjoy a safer ride in the cities. Larisa and Kalamata are two cities that consider the bikers more seriously and offer better solutions.
It’s prohibited biking in the highways but the options if you wish to travel by bike are plenty. It is as safe as it can be if you consider that you share the road with cars and trucks. The Eurovelo network has Greece as a member but the infrastructure is poor. There are 3 Eurovelo Routes (8,11 & 13) but they are not realized yet. You can read more about these routes here.