When we tried out two-point perspective
, we found that we needed two vanishing points and two sets of lines to draw horizontals moving away from us in each direction. To draw them in three point perspective, we just need to add an extra vanishing point, which is at a point above (or below, if you're drawing something looking down). Tracing the edges and lines on this tower and extending them out, we can see the vanishing lines heading off in each direction - eventually they meet at the vanishing points. The lower two vanishing points won't fit on the page. They'll also not be level, as the horizon would be in standard two-point, because the view is at an angle - that's a whole lesson for another day!