A former urban explorer says the most unpleasant part of exploring New York City’s sewer system was the cockroaches, not the rats, smells or ever-present dangers. Steven Duncan reflected this week on his years documenting the subterranean networks running under New York and other world cities after groups of people were captured on surveillance videos popping in and out of sewers in Brooklyn and Queens in recent days. Duncan believes the groups were likely traversing the large, 19th century sewer mains that run underneath parts of the city. Officials stress it’s not just illegal to enter the sewers but also extremely dangerous.