Why does Finland have so many lakes?

Ice. Finland has about 188,000 lakes, and essentially all of them are glacial - the Scandinavian ice sheet scraped the landscape down to bedrock, gouged out hollows, and dumped moraine that dammed the drainage as it retreated around 10,000 years ago. The result is a country that is roughly a tenth water and almost entirely flat.

The land is still recovering from the weight. Kilometres of ice pressed the crust down, and it has been rising back ever since - up to about a centimetre a year on the Gulf of Bothnia coast, which is fast enough to matter. Finland gains something like seven square kilometres of new land from the sea every year, harbours become too shallow within a human lifetime, and there are medieval churches built on the shore that now stand well inland.

That rebound also creates a legal oddity nobody else has to deal with: who owns land that did not exist when the boundaries were drawn. Finnish and Swedish property law has rules for emerging land, and coastal municipalities periodically acquire territory without anyone doing anything. The country is very slowly getting bigger.