by airplane - airport: Amsterdam Schiphol, then a train to Groningen. Unfortunately, there is no convenient direct flight to Groningen.
At Amsterdam Schiphol the railway station is easy to reach via walking following the signs: "Naar de Treinen." There is a regular train 2 times an hour. If you take the right direct train, you can get to Groningen in about 2 hours, otherwise you have to change trains in Amersfoort - just the other side of the platform, there is hardly a waiting time. When in the train, ask the conductor to make sure you are in the right part of the train that goes to Groningen. The train splits in Zwolle station; the front part usually goes to Groningen, whereas the rear part goes to another city (Leeuwarden).
by train : Groningen Central Station. The reserved hotels are either in the centrum or near the conference center Martiniplaza. The centrum is an easy walk straight across the water in front of the Railway station, cross the small pedestrian bridge. Mercure and the HampshireHotelPlaza Groningen are in South-East and South direction from the railway station. For these hotel best is to take a taxi, it is an about 10 minutes drive.
by car : freeways to Groningen