CNN — Descending up to 40 meters beneath the Baltic Sea, the world’s longest immersed tunnel will link Denmark and Germany, slashing journey times between the two countries when it opens in 2029. The first tunnel element of the Fehmarnbelt Tunnel was inaugurated June 17 by King Frederik X of Denmark, in what was a milestone moment four years after construction began in 2020, with more than a decade of planning preceding that. On the Danish side, east of Rødbyhavn, the factory that will build the...