Dundee? Check your clues again. Their bridge came down in 1879. McGonagall wrote a hilariously bad poem about it.
Anyway the sticking point right now is that you can only be right if the earth is flat. So to convince us, you need evidence that the earth is flat. But fear not, there is a way:
At the equinoxes, the sun moves across the sky directly above the equator, right? Thus it appears to travel around the earth and ends up back where it started after 24 hours. So the equator is a circle. Okay so far?
Well if the earth was round, the equator would just be the familiar hoop around the earth's middle, but if the earth was flat, the equator would be a big circle on the flat ground.
So if you go to somewhere on the equator, Singapore or Quito for example, with a piece of chalk, you can mark the tip of the shadow of a flagpole or lamp post every hour from sunrise to sunset. If the earth is flat, joining the chalk marks will show the distinct curve the sun follows as it circles us. If the earth is round the marks will describe a dead straight line.
Simple, isn't it? It's astounding no flat-earther has ever demonstrated this to a disbelieving world.