<p>An interturbine duct (12) for interconnecting a gas turbine engine (10) with a power turbine (11). The interturbine duct (12) is of generally frusto-conical form and double skinned so that an annular cross-section volume (20) is defined between the skins (18,19). Cooling air introduced in a generally tangential direction at the larger diameter extent of the duct (12) follows a generally spiral path to the smaller diameter extent where it is exhausted into the efflux of the gas turbine engine 10). The spiral path of the cooling air ensures good heat transfer coefficients over both of the skins (18,19) and obviates the need for baffles to direct the cooling air flow.</p>