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Busses are a cheap way to get around in Europe. If you don't fear a long voyage and want to come to Evoke for a more than reasonable price, this might be something for you.
There are many smaller bus companies reaching Cologne from all parts of Europe, but the most important is probably Eurolines, which has dependencies in 25 coutries, including the most Eastern Europe ones. Check out the dependence for your country, and make sure to book your tickets early to get some possible discounts.
The busses from Eurolines, as well as most other international ones, arrive at the Central Bus Station, which is located right behind the Central Trainstation (Hauptbahnhof). Enter the trainstation building and get to the partyplace as described on the train page.
Flixbus has daily connections to several German cities like Leipzig, Dresden, Bremen, Hamburg and Nürnberg. Check with their website for details and prices. One way tickets from Hamburg to Cologne start at 17 Euro (Regular 37 Euro).
Another operator is MeinFernbus which might be an alternative if you are coming from Stuttgart, Munich or Freiburg. Prices for a one way ticket Munich to Cologne start at 22 Euro (Regular 50 Euro).
Berlin Linien Bus
As the name implies, check with BLB when you are seeking a trip to Evoke from Berlin. Prices for Berlin to Cologne start at 33 Euro (one direction).