Ever since Greg Young became one-half of “The Bowery Boys,” the podcast about New York City history he started with his friend Tom Meyers in 2007, visitors to the Big Apple have sought out his tourism recommendations. Forgoing Manhattan, Mr. Young, an amateur historian and Missouri native, sends them to the outer boroughs, to sites that are “offbeat but still truly unique to New York City and not overrun with crowds.” And they are outdoors, a plus for the summer ahead.