Sketch of the observed central structures. The K-band emission traces the inner rim of a thin disc of hot gas and dust, at or close to the dust sublimation radius r ≈ 0.24 pc. The inner water masers are cospatial with the hot K-band dust. The masers stretch out to r ≈ 1 pc (Gallimore et al. 2001). MIR observations show warm dust on similar scales as the outer masers (e.g. Raban et al. 2009), likely originating from the disc periphery. ALMA observations of HCN and HCO⁺ show a turbulent structure, which rotates in the opposite direction as the maser disc (Imanishi et al. 2018). The v_c/σ of the molecular gas structure argues for a thick disc, which contains enough gas mass to reach column densities of N_H ≈ 10²³ cm⁻² that screen the central region by A_V ≈ 90 (A_K ≈ 5.5) from the observer.