If you arrive at Schiphol Airport, it is still a 2.5 hour trainride to Groningen. Check the Dutch Railway website for timetables. It is either a direct connection, or there is just one transfer at the station of Amersfoort. Note that at Schiphol there are also ticket machines at the platforms, and not only in the luggage halls (to avoid possible queues).
Within the city of Groningen everything is within walking distance. The trip from the station to the hotels is about 1 kilometre. However, if you feel like taking the bus, you can look up connections at http://journeyplanner.9292.nl/. A useful ticket is the "Euro-ticket", which you can get for exactly one coin of 1 euro (no smaller combinations) from the driver. It is valid for 1 hour within the whole of the city.
Below you can find a map of downtown Groningen. The trainstation, conference site, both hotels, the locations of the public lecture, conference reception and dinner are indicated.
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