Cologne International Airport (CGN, 30 min to Central Cologne) and Frankfurt International Airport (FRA, 60min to Central Cologne) provide many direct international connections. The central train station (Köln Hauptbahnhof) connects Cologne with the European fast track rail system (e.g. 2h from Brussels; 3h from Paris, Amsterdam, Freiburg; 4h from Berlin, Hamburg, Basel; 5h from Munich, 6h from Zürich, Bern, Lyon). The conference site is directly next to Cologne south station (Köln Süd).
From CGN aiport to Cologne or Cologne South (where the conference is) you can use frequent public transport trains, see www.bahn.de. For this journey you need the regional ticket "Preisstufe 1b (CityTicket)", which costs EUR 2.80. There are several ticket machines at the station.