Kythnos is a lovely destination in Cyclades that is really worth visiting! You can only reach Kythnos by ferry, from Piraeus and Lavrio ports in Athens but also from other islands of the Aegean. The closest airport is the International Airport of Athens.
There is a regular ferry connection between Kythnos and Athens. Ferries depart from Piraeus and Lavrio, two of the 3 ports of Athens, and the trip lasts about 1.5 to 3 hours. Kythnos is also connected with some other islands of the Cyclades, like Kea, Sifnos, Milos, Paros or Santorini.
There is no airport on the island of Kythnos. The closest one is Athens International Airport “Eleftherios Venizelos” which receives both domestic and international flights all year round. From the airport of Athens, you can easily reach Lavrio port and embark on the ferry to Kythnos.