The Øresund Bridge is an underground tunnel that travels underneath the Øresund strait, a body of water between Sweden and Denmark. This tunnel allows a railway to connect the two countries and provides easy transportation between the two nations. Not only is it efficient, but this underwater underground tunnel is also somewhat magical. Riding on the bridge, you will find yourself seemingly pulled underwater only to emerge on the other side in another country.
Not only is this an excellent transportation system, but it shows off Sweden's skill at civil engineering and the wonders the country has created with regard to its infrastructure.