Switzerland's Gotthard Base Tunnel is world's longest and deepest tunnel
The Channel Tunnel, between the UK and France, has world's longest undersea section
This year marks the 20th anniversary of the opening of the Channel Tunnel linking France with the United Kingdom, and the 50th anniversary of the deal which led to its creation.
The Gotthard Base Tunnel, dubbed Switzerland’s “construction of the century,” was 17 years in the making and is reported to have cost around $12 billion.
To mark the occasion, we’re taking a look at some of the world’s greatest tunnels.