If you arrive by Plane

There is a special airport bus from Bologna Marconi Airport which takes you into the centre of Bologna.

It leaves every 15 minutes during the day from outside the arrivals hall.  The first bus is at around 6am in the morning and the last one at 23.40. 
The bus is called BLQ and is easily identified as it is grey and light blue in colour as opposed to the orange urban buses. 
The fare from airport to the centre is 5 euros per person and you can pay the driver directly on the bus. Although a ticket machine is situated at the bus stop it is not necessary to buy a ticket before you board.
The journey from the airport to the railway station takes about 20-25 minutes, depending on the traffic.  There are three intermediate stops before the station one of which is in via Ugo Bassi and the others are both in via Dell' Indipendenza Teatro Arena del Sole is the exactly bus stop to arrive at Hotel Metropolitan  an Met's Apartment, one at the end nearest Piazza Maggiore and the other a little over half-way up the long street.

 
There are also taxis available outside the airport.