Image distortion - what causes this???

Can anybody pls tell me why there seems to be so much image distortion in this pic?
Taken with Oly OM-D with Panasonic 45-175 x zoom lens at max zoom.

Every wall/straight line is badly distorted. Is it normal for a long shot like this due to refraction or just the air density or is it a lens or camera problem?

Many thanks for your ideas/comments.