Perspective distortion occurs when you point the camera towards the subject at an upward angle. The effects are most evident with a wide angle lens and architectural details. Buildings and towers appear to be leaning or falling over. To correct for this, start by moving further away from the structure. This will allow you to hold the camera parallel to the structure, greatly reducing the issue. If more adjustment is needed, you can then use the perspective tools in Lightroom to fine tune the angle.