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That must be one heck of a bathtub!

Oprah Winfrey journeyed to an orthodox Jewish congregation in Brooklyn Heights to take a gander at the shul’s state-of-the-art mikvah — a ritual bath for religious Jewish women.

“It’s a very spiritual thing,” said synagogue member Ed Weintrob. “You’re supposed to build a mikvah before you build a synagogue.”

Winfrey chose the “chosen people” to film a segment of her new TV show “Oprah’s Next Chapter,” and visited both Borough Park and Brooklyn Heights to hang out with some Hasidic Jews.

Residents gathered outside to catch a glimpse of the TV baroness, though, face it, jaded Brooklyn Heights residents have seen a few bold-faced names in front of the Remsen Street shul (yes, we are talking about you, former Israeli Foreign Minister Tzipi Livni!).

A mikvah is a traditional bath drawn from natural water sources — in this case filtered rain — where Orthodox women go after their menstrual cycle to cleanse themselves before resuming “relations” with their husbands.

Winfrey’s getaway vehicle drew a crowd of gawkers to Remsen Street. Community Newspaper Group / Eli Rosenberg

An archaic tradition? Religion-backed misogyny? The rabbi begs to differ.

“This is the best thing for a marriage,” said Rabbi Aaron Raskin, who leads the orthodox congregation and has been married to the same woman for 22 years. “Absence makes the heart grow stronger.”

Winfrey did not bathe in the mikvah, though it is open to women of all religious persuasions. Her new show “Oprah’s Next Chapter,” will premiere on her OWN Network in January and will feature interviews with spiritual leaders all around the world.

Oprah may be a god on TV, but the religious folks in Brooklyn Heights were only faintly aware of her.

“I have never even seen a single one of her shows,” admitted Bronya Shaffer, who showed Winfrey around the mikvah. “When I told Oprah’s producer that I didn’t know anything about her work, she said, ‘That’s refreshing!’ ”

Reach reporter Eli Rosenberg at erosenberg@cnglocal.com or by calling (718) 260-2531. And follow his Tweets at @from_where_isit.