Zombie survival mod DayZ takes place in the nation of Chernarus, which sounds entirely made-up, but it's only mostly made up. The geography of the map is actually lifted from a real-world location, around Povrly, in the north of the Czech Republic.
Sure, there's no ocean in the Czech Republic (only ArmA/DayZ devs Bohemia Interactive), but as you can see from this comparison here, the real Povrly's river matches the outline of the fictional Chernarus' coastline almost perfectly. As does the rest of the terrain, right down to the location of towns and even buildings. It's so close, in fact, that aside from the names of the towns, you could use the game's map to navigate the actual location in the real world.
Which is what makes this cosplay expedition so awesome. They're not only in costume, complete with authentic props like guns, beans and, um, soda, but they're walking the actual roads and actual hills featured in the game/mod. There aren't many video games that let you get that into something.