The Bosporus Strait.
The Bosporus Strait, and the Dardanelles Strait.
Istanbul, in turkey
There are actually 2 straits that separate them, they are the Bosporus and Dardanelles Straits
There is not a specific definitive border between Europe and Asia, since they're on the same tectonic plate. Russia is part of both continents and the dividing points between Europe and Asia are...