They say becoming a parent changes everything and it has. I’ve learned to live on less sleep, love deeper than I thought possible and feel empathy for things I may not have before. It also changes the world around you. My wife Rachel and I live in New York City with our 4-year-old son Sam. A quick-witted, quirky firecracker, with a killer smile and an infectious laugh.

Living in a great big metropolis we sometimes worry that there is too much stimulus, and finding space and quiet time can be a challenge. But for the most part Sam has adapted to city life like a champ, embracing his action-packed environment to the fullest. What Rachel and I sometimes see as overload, he sees as the next adventure.

There is no shortage of construction sites to admire and buses, trucks, taxis, and planes to follow. For a period of time Sam had a deep and passionate love affair with garbage trucks. He was even a garbage truck for Halloween one year. But that relationship seems to have run its course, and his latest love has reached a level his garbage truck admiration never had.

Like a lot of boys his age, Sam loves trains. But our son specifically loves the New York City Subway system. It’s all he talks about. His aunt recently gave him a book of subway systems around the world, so he’s dabbled in Boston (where his parents grew up) and London (a city we know and love) but his first love is for the New York City Transit System. He has subway dreams at night. The free maps they hand out at the stations are prized treasures, fanned out over every free inch of space in our apartment. He collects wooden subway cars sold at this city’s Transit Museum and begins most days whizzing them around his train tracks reciting to an imaginary audience of riders the familiar mantra of the subway conductors: “Ladies and gentlemen, this is a Brooklyn bound B train … the next stop is 86^th St. Stand clear of the closing doors, please.”

From studying his maps, and he does study them, Sam easily drops names like “Flatbush Avenue Brooklyn,” “Canarsie St,” “Inwood,” and “Far Rockaway” — places he really shouldn’t know at this stage of the game were it not for his undying love for all things subway. He likes to know where every train begins and ends and has committed a good portion of the map to memory. On occasion a fellow passenger will ask if I know whether the train we’re on makes a certain stop. On more than one occasion I’ve been unsure, so I turn to ask our 4-year-old who knows with certainty whether it does or not. We’ve gotten some funny looks, and awkward smiles, and generally people don’t seem to trust that a 4-year-old knows the subway, but I know.

We’ve yet to see a downside to Sam’s subway interest. He’s learned the number and letter systems. He’s beginning to understand maps and likes to study the way tracks come together, and so we indulge his latest obsession. We often joyride the subway as a family on weekends. It’s a cheap thrill, that’s for sure, and a great way to explore the city we’ve lived in for 20 years through completely different eyes.

My wife once took Sam on an epic 3-hour subway tour, trying to hit as many different trains as they could. As of late, Sam and I have been trying to complete every stop on various lines, one train at a time. It’s become a ritual on the days I’m able to pick Sam up from school. We have a routine, boarding the first car on every train so we can peer through the front window and follow the train’s course.

We’ve admired the Statue of Liberty from “South Ferry,” last stop on the "1" train. We’ve visited “Flatbush Ave,” last stop on the “2” line and “Wakefield” where the “2” is no longer “sub” but an elevated line.

Fifteen years ago I was running from hell as the World Trade Center began to collapse. Recently I was back with my boy, checking out the stunning reflecting pools where the towers once stood, running around the newly planted trees. It was a beautiful thing, made possible by our quest to reach “World Trade Center,” last Stop on the “E.”

We’re eagerly anticipating the opening of the new “T” line. It’s New York’s first major expansion of the subway system in over 50 years. Yes, I know things like this now. I imagine we’ll be lined up like groupies waiting to be one of the first to ride.

I recently mentioned to Sam that wearing his 1 train T-Shirt on the 1 train was a little like wearing the concert T-shirt to the concert, not cool. He doesn’t see it that way. We’ve even made friends with the one of the “1” conductors we see on a regular basis. (Hey Donnie!) When Donnie sees us in our usual spot at the end of the platform, he knows to take down his backpack, which he hangs from the front window, so we have an unobstructed view. That’s New York City at its best.

There are days I’d rather not be underground. And days I insist it’s “too nice” to be riding the subway. Sam argues that he thinks it’s “too nice” underground. I often cave, because I know there will come a time when we won’t have this time together, and so I just sit back and enjoy the ride.

On Father’s Day, when lots of Dads are firing up the grill, or playing catch in the yard (we love to do those things too), you might find me and my family riding the subway “just for fun” and I wouldn’t have it any other way.