A fun idea that came to me the other night. Take 2 real-world countries and combine them together in some way to make a new one. This is open to a number of different variations and ways to interpret it. You could physically take the coastlines/borders and smash them into each other, you could take the geography/cultures of each country and use them to inspire a brand new one, or I'm sure there are many other interesting directions people here could take it. I feel it would work better leaving the country options open as then it allows for some more varying combinations. You could go for two very different countries, the sharp Norwegian fjordland full of dense Amazonian rainforest, or match more similar terrain, the mountains and lochs of Scotland matched and paired with Finnish lake-country.
For those who are less interested in regional/continental maps I guess we could extend this to the option of fusing cities/towns and see how people marry two cultures together in that way.