The Silfra fissure is a lake located within the heart of Thingvellir National Park in Iceland that was formed in 1789.
It is the only place in the world where you can swim or snorkel between two continents.
In some cases the space is so narrow, you can touch North America and Europe at once.
The water is super clean because the river feeding this lake was overrun by a volcanic eruption thousands of years back. The pumice from the eruption blocks the river and as such cleans the water that runs through the lake.
The North American and Eurasian tectonic plates are said to be moving apart at the rate of 2 centimetres per year.
And, it can also take 100 years for the water in this lake to travel 50km.
It is, indeed, a geological wonder.
Footnote: Swim between two tectonic plates