Tymara Walker, 38, gave an impromptu performance of "O Holy Night" in Union Station on Dec. 3. Now, the video of her singing has gone viral. (Instagram @itruph)

Good things don’t often happen inside Metro stations — and that’s what makes this impromptu Christmas subway performance all the more surprising.

Tymara Walker, 38, is a professional singer from Las Vegas. She and some family members visited the District earlier this month, taking a whirlwind Saturday tour of the city.

At the end of a long day, after navigating their way to the Red Line platform at Union Station — “We were all so anxious about catching the right train!” Walker recalled this week — she had an idea.

Walker wanted to sing. Specifically, she had the urge to sing “O Holy Night.” She asked her daughter to hold her phone and turn on the camera.

“The acoustics are great,” Walker said, “and I thought I’d give it a try.”

Spoiler alert: It turns out that Walker is really, really good.

Now, the video of Walker’s soaring vocals bouncing around inside a dingy Metro station has gone viral: It has been viewed more than 300,000 times on Facebook.

“Yessssssssssss she killed that!!!!!!!!!!! Beautiful voice,” wrote one of the thousand people who have commented on the video.

I listened to this like 30 times,” wrote another commenter. “Her voice is so pretty it brings tears to my eyes!!

“Amazing! Her voice is so clear!!” added one D.C. resident. “Hate having to take the Red Line though! Yuk!!!”

Walker was in town for a singing gig in Northern Virginia. Back at her home in Las Vegas, she’s an on-call performer for the Michael Jackson ONE Cirque Du Soleil show. She also spent two years performing as a background singer for Gladys Knight. So she doesn’t get nervous about performing in front of a crowd. Her family members are also musical: Her mother, her younger sister and a good friend are singing in the background of the Union Station video.

“We were all raised in church,” Walker added. “That kind of stuff just comes natural.”

Walker said there have been a lot of life circumstances of late that moved her to want to hold an impromptu one-song performance in a Metro station. After years of hardship — an abusive relationship, a traumatic divorce and then a period of homelessness as she worked to get back to financial independence — Walker said things had finally started looking up in the past year. She’s remarried now, “to my Superman hero.” She has steady work doing what she loves: singing. And she felt as if she could finally afford to buy some nice things for her children for Christmas.

“This is the first Christmas I’m in a position that feels like a fresh start,” Walker said. “That’s why I sang.”

The reaction she got from the crowd at Union Station was pretty similar to what she has received online: tears, applause and effusive praise.

“People started to clap and cheer,” Walker recalled. “Everyone was smiling. One lady was wiping tears. It was really beautiful.”

One man listening on the train platform told her that she should record an album.

“I yelled back, ‘I have a single, go buy it!'” Walker said.

Her videotaped performance has been featured on French television, and the tweets and Facebook comments keep rolling in. Walker says she’s hopeful that her spontaneous Metro appearance might be the start of even bigger things.

“All of my struggles and accomplishments are working together to show my children that no dream is too big. I went from singing in little churches in Toledo and Detroit to flying on the moon in the Michael Jackson ONE show for Cirque,” Walker said. “So mommy just needs to win this Grammy … so we can bring it full circle!”