⁵⁷Fe Mössbauer spectroscopy was used to study single-crystals of K_0.8Fe_1.76Se_2.00 from 6 K to 673 K. At 6 K, the hyperfine field (B _hf) is canted away from the c-axis by 18 ± 3°. The temperature dependence of B _hf follows a spin wavemodel with a spin excitation gap of 9 ± 1 meV. A sudden increase in the linewidth and a corresponding drop in (1/2)eQVzz at T_N  = 532 K are indications of strong coupling between the magnetic and structural transitions.