This undated photo provided by Steve Duncan, shows the Canal Street sewer in New York. Steve Duncan via AP-Yonhap

NEW YORK — It wasn’t the rats. Or the smells. Or the germs.

No, the most unpleasant part of descending into New York City's vast sewer system, according to former urban explorer Steve Duncan, were the cockroaches.

“They’re all over the place, crawling on walls, dropping down on you,” Duncan recalled this week. “They were the worst.”

Duncan, 48, who now lives in Maryland, reflected on his years documenting the muck-filled tunnels running under New York after surveillance videos captured small groups of people mysteriously entering and exiting the sewer system in Brooklyn and Queens in recent days.