But few chapters from the system’s past so rankle the transportation authority, which declined to discuss the station in detail. For one, the authority is mindful of persistent calls to restore F express service in Brooklyn, fearing that any mention of the station might convince riders that it could be renovated adequately. Officials also noted security concerns and a desire to “discourage urban explorers” from venturing underground.

At City Hall, though, a sense of adventure is celebrated. On the authority’s website, members of the New York Transit Museum are encouraged to buy $40 tickets for a tour of the station, referred to by its nickname, “the Jewel in the Crown.” There are two sessions in December.

For the 100th anniversary of the subway system in 2004, the station, which was closed in 1945 because its platforms could not accommodate 10-car trains, was reopened for a ceremony with Mayor Michael R. Bloomberg. Workers dressed in turn-of-the-century outfits, as Mr. Bloomberg helped maneuver a vintage four-car train.

Less elaborate outings have also been condoned. Though conductors were in the past known to expel passengers at the end of the No. 6 line, announcements on many trains have been adjusted to reflect a change. “The next stop on this train will be Brooklyn Bridge-City Hall, on the uptown platform,” the message now says, in a nod to riders who might remain on board. The cost for them, of course, is that of a single ride.

Even the pace of the train is cooperative, at least compared with the express-powered blur past Bergen Street. A recent, unhurried rumble through the loop revealed the skylights, the faience signs, the arched entryway illuminated by six temporary bulbs.

“It’s a salute to an era when subways were meant to enhance the quality of life in the city,” said Gene Russianoff, a longtime transit advocate for the Straphangers Campaign. “I guess they do now, but not with beautiful stations.”