From the bus stop Siegen ZOB (main station) take the bus (SB4, SB5, R12, R13, R14, C103) to the bus stop "AOK" and walk a few meters back along Spandauer Str. (B54) to the building.
From the HTS exit Hauptbahnhof, take the B54. Continue straight ahead for some time. Then turn left into Löhrtor. Behind the indoor swimming pool, turn right into the parking garage.