A wind turbine (1) comprising a tower (2) and one or more nacelles (3) mounted on the tower (2) is disclosed, at least one of the nacelle(s) (3) housing one or more drive train components (9,10,11) and a transportation system for moving drive train components (9,10,11) of the wind turbine (1). The transportation system comprises one or more sliding rails (15) configured to carry a drive train component (9, 10,11) during movement, and one or more sledges (19). Each sledge (19) is movably connected to a sliding rail (15), and configured to be attached to a drive train component (9,10,11), thereby allowing the drive train component (9,10,11) to move along the sliding rail(s) (15). Each sliding rail (15) comprises two or more rail modules (6,13,14) being detachably connected to each other along a direction of movement defined by the sliding rail (15).