Bus and Tram.   Tickets for public transportation must be bought before getting on the bus or tram; there is a vending machine at each stop. You must buy a 2.20 CHF ticket, with which you may travel within two zones for 60 minutes (e.g., from the airport to the university). You can also use Euro (1 Euro = 1.40 CHF).
Caution : the vending machine won't give you change.
A ticket for one zone and 30 minutes costs 1.80 CHF.
A ticket for two zones that it valid for the whole day costs 6.- CHF.
You can also buy a card for 20 CHF with which you can get the tickets at the vending machine.
You can find here a map of Geneva.

Railway.   Trains coming from Lausanne usually continue to "Genève Cointrin" station, which is in the airport. You should get out at "Genève Cornavin", which is the main station and in the center of the town.

Taxi.   A ride from the railway station to the University, or to one of the usual hotels, costs about 20 CHF, from the airport about 35 or 40 CHF.

From the Airport "Genève Cointrin" to

•  UNI-MAIL:  take bus no. 10 (it's an ordinary city bus), which leaves from the "Departures" floor, one floor above the "Arrivals" floor. Get out at the stop "Bel-Air". Then, take bus no. 4 and get out at the stop "Uni-Mail". The trip will take a little bit more than 30 minutes and costs CHF 2.20.
  
  
•  Section de Mathématiques:  take bus no. 10 and get out at the stop "Bel-Air". Then, take bus no. 4 and get out at the stop "Acacias". Cross the street and walk about 50 meters in the same direction: 2-4 rue du Lièvre, 2nd and 6th floor.
  
  
•  Hotel Grenil (7, Avenue Sainte-Clotilde, 1205 Genève)  take bus no. 10 and get out at the stop "Jonction"; cross the street, follow the "rue du vélodrome" and a few metres on "Bvd. Carl-Vogt"; then turn left into the "Ave. Sainte-Clotilde".
  
  
•  Hotel Carmen (5, rue Dancet, 1205 Genève)  take bus no. 10 and get out at the stop "Bel-Air"; then, take bus no. 4 and get out at the stop "Uni-Mail"; cross the big street and you are in the "rue Dancet", where the hotel is located.
  
  
•  Hotel Caroline (rue Caroline 51)  take bus no. 10 and get out at the stop "Bel-Air"; then take tram no. 12 (direction "Bachet") and get out at the stop "Armes", cross the "Place d'Armes" and find the "rue Caroline".
  
  
•  Hotel Comédie (12, rue de Carouge, 1205 Genève)  take bus no. 10 and get out at the stop "Bel-Air"; then take tram no. 12 (direction "Bachet") and get out at the stop "Plainpalais", and walk about 50 metres in the same direction; see also the map: 
  
  
•  Hotel Aïda (6, avenue Henri-Dunant, 1205 Genève)  take bus no. 10 and get out at the stop "Bel-Air"; then take tram no. 12 (direction "Bachet") and get out at the stop "Plainpalais", turn right and find "avenue Henri-Dunant".
  
  
•  Hotel St. Gervais (20, rue des Corps-Saints, 1201 Genève)  take bus no. 10 and get out at the stop "22-Cantons"; see also the map: of the homepage of the hotel 
  
  
•  Hotel Dizerens (3, rue Dizerens, 1205 Genève)  take bus no. 10 and get out at the stop "Bel-Air"; take tram no. 12, get out at the stop "Augustins", and walk back about 50 meters to the rue Dizerens.
  
  
•  Studio House Acacias (4, route des Acacias, 1227 Genève):  take bus no. 10 and get out at the stop "Bel-Air"; then, take bus no. 4 and get out at the stop "Acacias". Cross the street and you are there.
  
  
•  Pension Esmeralda (7, rue Simon-Durand, 1227 Acacias/Genève):  take bus no. 10 and get out at the stop "Bel-Air"; take bus no. 4 and get out at the stop "Acacias". Cross the street and follow the "rue Caroline" for 300 metres; then turn right into the "rue Simon-Durand".