The Dead Sea is the lowest point in the world at 394.6 m (1269 ft) below sea level. It therefore has no outlet — water only leaves by evaporation — and is extremely salty. It gets its name from the fact that the water is far too salty for anything to live in it.
This sea is an interesting place to swim because the salt makes the water denser so swimmers are more buoyant. Also, unlike many other beaches, the chance of encountering dangerous marine life is zero.
The east and west coasts are in different countries and in different articles here: