(This is not the math department, but a lecture hall on the main university campus.)
Conference venue
Math department, University of Duisburg-Essen
Hotel B & B
Hotel Flowers Hotel
Hotel Motel One
Frohnhauser Str. 55
45127 Essen
Email essen@flowershotels.de
Phone +49 201 246790
Most of the relevant places (hotels, university campus, possibly the math department) are in walking distance from each other. To cover larger distances, you can use the subway (U-Bahn), tram (Straßenbahn) or a bus.
The closest subway stop is "Universität" (lines U11 and U17). Depending on where you come from you could enter the subway at the main station (Hauptbahnhof), at Hirschlandplatz or at Berliner Platz.
For travelling inside Essen (this includes all hotels, the university, restaurants etc. mentioned here), you need a ticket for Zone A2. For the ride from Essen central station to Berliner Platz or Universität Essen it is enough to buy a ticket Zone K ('Kurzstrecke', short distance). Note that a Zone K ticket is valid only for 3 stops. Single A2 and K tickets are valid for a ride starting right after you buy the ticket; you cannot buy them in advance for later rides. For buying tickets in advance, take a ticket for four trips; those tickets must be stamped when you enter the train, at the machines inside the train. (If you change trains, you do not need to revalidate the ticket.)
Tickets can be bought at ticket machines in every underground station and at every tram stop, or in the EVAG centers in the underground station of the central train station, or at Berliner Platz.