The journey into London’s new sewer system begins with a safety briefing and a wardrobe change — a hard hat, goggles and gloves, steel-toe boots, high-visibility orange trousers and matching shirt. Then comes the 40-meter (131-foot) descent in what looks like a shark-diving cage dangling from a crane beside the yawning hole next to the River Thames.

“When you get to the bottom, it looks like Gotham City,” Scott Hughes, the section manager at the worksite, tells a group of three community leaders touring the almost-finished Thames Tideway Tunnel project below.