Kavala is the port of eastern Macedonia, at the far north-east of the country, and there is no ferry from Piraeus because the seas do not connect that way. It is a flight or a long drive, and it is the car ferry port for Thassos just offshore.
Diagram by Greece Trips. Free to reuse with credit - CC BY 4.0.
By air
The sensible option for most trips. Kavala is served by an airport a short way from the city, with domestic flights from Athens and some seasonal international services, which exist largely because of Thassos.
If Thassos is the destination and you are not bringing a car, flying here and taking the short crossing is much the easiest route.
By road
A long day. The motorway runs north to Thessaloniki and then east along the coast, and it is good road most of the way.
We print no drive times, because they depend on the traffic leaving Athens, the season and your own pace. What is worth saying is that this is a journey to break rather than to do in one push if you have any choice, and Thessaloniki or Volos are the obvious places to break it.
The reason to drive is Thassos: the crossing takes cars, and the island is built around a ring road. If you want your own vehicle on the island, driving up beats hiring twice.
By rail
The railway reaches this part of Greece, though not to Kavala itself, and services have been variable. Trains in Greece covers what the network does and does not do; do not plan a tight connection on it without checking current operations.
Why there is no ferry from Piraeus
Worth a line because people look for one. Piraeus serves the Aegean south and east of Attica. Kavala sits on the north Aegean coast, and the sea route between them exists but is not a passenger service anyone runs for travellers.
The north Aegean island line from Piraeus reaches Chios, Lesvos and Limnos rather than the northern mainland ports.
Once you are there
Kavala has a monumental aqueduct, the Kamares, running on two tiers of arches straight across a modern street between the old town and the new, and the Panagia quarter climbing a headland to a castle above the bay.
Philippi is a short drive inland and is one of the more substantial Roman sites in northern Greece. Thassos is a short car ferry offshore. Day trips from Kavala covers both.
Diagram by Greece Trips. Free to reuse with credit - CC BY 4.0.
Where this leaves you
Fly if you are going to Kavala or to Thassos without a car, drive if you want your own vehicle on the island and can give the road a long day. There is no ferry from Piraeus and there is no need for one. Break the drive at Thessaloniki rather than pushing through, and give the city a night rather than treating it as a ferry terminal.
Quick answers
Is there a ferry from Athens to Kavala?
No passenger service that travellers use. Piraeus serves the Aegean south and east of Attica, and its north Aegean line reaches Chios, Lesvos and Limnos rather than the northern mainland ports. Kavala is reached by air or by road.
How long does it take to drive from Athens to Kavala?
It is a long day on motorway north to Thessaloniki and then east along the coast. Times depend on traffic and season, so check a routing service rather than a printed figure, and consider breaking the journey at Thessaloniki.
Should you fly or drive to Kavala?
Fly if the city or Thassos is the destination and you do not need your own car. Drive if you want your vehicle on Thassos, since the crossing takes cars and the island is built around a single ring road.
How do you get to Thassos from Kavala?
By a short car ferry from the port, which is why Kavala fills with vehicles from northern Greece and the Balkans in summer. It is one of the easiest Greek islands to reach with your own car.