You can take a train from Moscow, St. Petersburg, or Petrozavodsk along the Oktyabrskaya railway to Belomorsk station.
Information about train schedules, ticket prices, and availability can be found on the following websites:
Russian Railways: http://rzd.ru
Petrozavodsk Transportny: http://www.ptz-trans.ru/
Petrozavodsk — Belomorsk (every day; twice a day — in the morning and evening).
Petrozavodsk — Belmorosk; departure from Petrozavodsk at 16.00, arrival in Belomorsk at 22.00.
Belomorsk — Petrozavodsk; departure from Belomorsk at 04.00, arrival in Petrozavodsk at 9.00.
Book tickets by calling: 89114230208
By your own car:
Travel along Route M-18 «Kola» St. Petersburg — Petrozavodsk — Murmansk. Once you leave Petrozavodsk, drive along this route to the village of Pushnoy, then turn right in the direction of Belomorsk (38 km).
You can find a more detailed description of the route here: http://www.rutrassa.ru/federal/m18.php