Abstract: The present invention relates to a tower (12) configured to support a wind turbine (18, 20). The tower (12) comprises a mass assembly (22) suspended by suspension apparatus (24) from the tower (12) such that the mass assembly (22) is movable to and fro in relation to the tower. The tower (12) also comprises at least one coupling apparatus mechanically coupled to the mass assembly (22) and to the tower (12), the coupling apparatus being operable to couple energy between the mass assembly and the tower as the mass assembly (22) moves to and fro.