City of Joensuu locates about 450 kilometers to North-East from Helsinki and it is a capital city of North Karelia region with more than 75 000 inhabitants. City website: http://www.joensuu.fi/en/web/english
From Helsinki you can reach Joensuu normally by three different ways:
1. by airplane
Joensuu airport international code is JOE. Planes are landing to Joensuu several times every day , Sundays and July are the most quiet seasons.
Mostly planes are Finnair or Norra planes but tickets are always sold by Finnair or partner airlines. Ask your travel agency, you can fly to Joensuu example by Air France tickets etc. www.finnair.com. Helsinki airport locates in city of Vantaa, so name of airport is Helsinki-Vantaa. Believe or not: sometimes plane between Helsinki-Joensuu can be as cheap as train....
Airport of Joensuu is about 10 km from Joensuu center, busses and taxi cars are very quick going to city center after flight and to main bus station next to Sokos hotel Kimmel. There are good discounts in summer time with Helsinki-Joensuu flights.
In spring and summer time Ryanair is flying to Finland also. To Tampere from Bremen (Germany) and from Budapest (Hungary) / to Lappeenranta from Athens (Greece) and from Budapest (Milan Bergamo). Remember to check these flights from Ryanair.com website. From Tampere or Lappeenranta it is quite easy to take a train to Joensuu. Lappeenranta is closer to Joensuu than Tampere.
2. by train
Finnish trains are very comfortable and not very expensive if you buy your ticket in time. Finnish national railway company, VR, website is www.vr.fi
(they serve also in English). Cheaper "saver" train tickets are sold earliest 60 days before trip and I think latest about two weeks before your trip, if discount tickets are still available.
"Saver" tickets are about 25 €/one way. (Basic tickets are about from 41 euros to 56 euros /one way.) Sometimes you can get flight to Joensuu, with about same rate, specially in summer :-) .
You can take local train from Helsinki-Vantaa airport to Tikkurila or Helsinki railway station and jump to Joensuu train. Or you can take a Finnair bus from Helsinki airport to Helsinki main railway station. Local train is included to you train ticket to Joensuu.
If you want, you can also take also a train from Joensuu or Helsinki to Russian metropol St. Petersburg, before or after you visit. Of course you normally need a visa to Russia if you are EU citizen. Traveling by train to St. Petersburg takes about 3,5 hours.
3. by bus
Also one way (and cheap) to travel between Helsinki-Joensuu. Busses are ok to travel and tickets and timetables you can find from portal www.matkahuolto.fi
(also in English). You can travel also in the night, there is one night bus leaving from Helsinki-Vantaa airport to Joensuu about 2 AM (not in Saturday or Sunday), travel time about 8 hours.
From internet you can buy these bus tickets in lower price earliest 32 days before trip. Bought from a bus, ticket is little more expencive. Credit cards are not always accepted in matkahuolto busses, so prepare with cash.
Also low fare bus company, Onnibus, operates between Helsinki-Joensuu-Helsinki. This Onnibus company website you find from http://www.onnibus.com/en/index.htm. Cheap rate in one way can be example 15 euros (or cheaper) between Helsinki-Joensuu, depends how "early bird" rate you get. Onnibus does not accept cash, so you have to pay it by debit/credit card even in a bus. From airport you have to take train or bus to Helsinki center bus station (Kamppi, near Helsinki railway station) to get in the Onnibus going to Joensuu. Changes with timetables are possible, so follow them.