It takes 27 minutes to pass through the Gotthard Base Tunnel. It's something of a dreamlike experience: you're on the train hurtling through lush Swiss scenery – trackside haystacks and farmhouses, small villages with a single towering steeple, distant mist-crowned mountains, and dramatic landscape unfolding in more shades of green than you knew existed. Then all of a sudden, everything goes dark. Pitch black. You're still moving at about 150 miles per hour, but now you can't see where you're going.