Play the angles
Sigma makes two ultra-wide zoom lenses that take viewing angles to the extreme. They’re both rectilinear rather than curvilinear (fisheye) lenses, so aim to keep distortions to a minimum while really pushing the envelope of what’s technically possible. The Sigma 8-16mm f/4.5-5.6 DC HSM (£530/$700) is for DX-format cameras, while the Sigma 12-24mm f/4.5-5.6 II DG HSM (£600/$950) is for FX bodies. Both have built-in lens hoods.