A few years ago, the Turks laid a tunnel along the bottom of the Bosphorus (they didn't dig under the strait, they just ran it like a pipe). Now the European and Asian parts are connected not only by ferries and buses, but also by metro.

On this line, you can really feel the smell of dampness (unpleasant, really). And the fare is 2 times more expensive than on a regular line. But it's fast. Waiting for a ferry takes longer.