As a kid I remember learning that the US/Canada border is the longest undefended national border in the world, and I imagine this still holds true; I don’t think Russia and China have dropped their respective guards. So it’s kind of funny that one of the presidential candidates – I can never remember which is which – suggested that we need a fence along the border, perhaps to stem the hordes of Quebecois rushing south to steal all our Dunkin Donuts coffee because Tim Hortons’ isn’t as good.
If you’ve never been to New Hampshire’s northern tip, near the Third Connecticut Lake, you can find the border marked by markers in the ground that look like those the USGS puts on various peaks. One is shown above. Perfect for “left foot in one country, right foot in one country!” tourist photos.