The Department's address is Christies gate 17, 5007 Bergen.
From the airport you can either take a taxi to the Department (20-25 minutes, cost approx 300 NOK) or you can take the airport bus to the main bus terminal (85 NOK) and walk to the Department in Christiesgate (10 minutes, cost 0 NOK).
The train station ("jernbanestasjonen") is situated next to the bus terminal (100m); follow the instructions above.
Many of the streets in Bergen are one way so it is easy to get lost... However, all major roads leading into Bergen end up in the spaghetti junction shown on the left side of the map below. Untangle yourself from this junction and follow Fjøsangerveien (E39) directly towards the center of Bergen. When you have reached the city center and have Bergen bus station on your right side, chosse the left lane. Turn left and drive down Strømgaten. Stay in the left lane and make another turn to the left, and head down Lars Hilles gate. At the first intersection, take a right turn down Lyder Sagen Gate. From there, make a right turn and drive down Fosswinckelsgate. At the third crossing along this road, make a left turn and drive up Herman Foss gate. Turn right at next junction and follow this road until you reach "Muséplassen" outside the Museum of Natural History. Take a right turn here and you find yourself in Christies gate. The Department of Administration and Organization Theory are the first two buildings on the left side (Christies gate 17 and 19).
Note that due to major construction work being done driving routes change often enough to confuse even locals! It's best to get in contact with your host to get accurate directions before you attempt to drive into Bergen.