There's an unused subway station underneath New York's City Hall. Here's what it's like to visit.

As its name suggests, the subway station sits directly beneath City Hall, the oldest municipal headquarters in the United States. It's more than 200 years old.

The subway station was also beneath the City Hall Post Office and Courthouse Building, a massive French-style building that many derided as an eyesore. It was later demolished in 1939 to make way for what's today called City Hall Park.

The street cars on Park Row that crossed the Brooklyn Bridge (just out of view on the right) are long gone.

Here's how the tracks lie in relation to the City Hall building and the adjacent park. In this diagram it's easier to see how the 6 train makes its 180-degree turnaround while allowing express trains to continue south through downtown and into Brooklyn.

From above, it's nearly impossible to tell you're above a Gilded Age architectural marvel — but a trained eye could still see some of the skylights through the overgrown gardens in the park.

Unfortunately, both entrance stairways have been sealed as well, for security reasons, so we have to head over to the in-service platforms and get on a train that can let us off in the station.

We're doing this in the middle of rush-hour service, our tour guide reminds us, so we have to be quick when the train stops to let us off. Quickly after this train descends into darkness, our shuttle to decades past pulls in right behind it.

Those large gaps I mentioned earlier really are massive, and our tour guides bring over a ramp so we don't have to jump over live tracks.

Once on the platform, it really does feel like we've stepped back in time.

The hustle and bustle of trains just yards away is nearly silent. All of the street noise from above has been muffled. Dripping water, a near constant phenomenon in any subway station, is the only background noise to our tour guide's monologue.

A hard-to-read plaque commemorates the opening of "this first municipal rapid transit railroad of the City of New York"

This sign was impossible to see with the naked eye, but camera flash made it a bit better.

The station was designed by Rafael Guastavino — and it shows. The Spanish-born engineer is best-known for his arches, which can bee seen at other NYC landmarks like Grand Central Terminal and the Queensboro Bridge.

Guastavino was part of a larger movement known as City Beautiful, which flourished during the late 19th century and into the early 1900s. Many great buildings from the movement are landmarks in Chicago; Washington, DC; Cleveland; and Detroit.

Here's a closer look at the many layers of "Guastavino tiles" that make up a classic arch.

The skylights we saw from above are still functioning today — albeit with a few less tiles.

An even more elaborate skylight provided light for the original ticket hall.

The fare gates and ticket windows are long gone, but inside this vaulted room is where passengers would have paid their nickel to ride uptown to Grand Central Terminal, Times Square, and beyond.

Compared to some mega-stations, finding your way to the correct train was relatively simple here: just one staircase down to the platform!

If you noticed some people covering their ears in the previous photo, it's because trains that pass through the station during regular service are loud. Very loud.

Rail squeal occurs when train go through sharply curved portions of the track. You can also get a better sense of the platform gaps as this train passes through.

If this were a normal subway station, we'd be able to exit or enter through these stairways. Unfortunately all I found at the top was a padlocked door.

Overall, the station is in good shape, but it may never be returned to its former glory. Here's how it looked on a postcard at the time.

Tours aren't the only thing the Transit Museum does. It's one of the city's lesser known museums, but it has plenty of options for fans of historical transit.

Every winter, the museum runs a "shopper special" train on weekends to ring in the season.

You can read about the antique trains, courtesy of Business Insider's Ben Gilbert, here.