The British star took a break from filming 'The New Pope' to show her the amazing city.
Law, 46, and Coan, 32, were both in great spirits as they rode in the unique taxi together.
The two wrapped up from the cold weather as they boated around the City Of Bridges.
The couple has been dating for four years and they seem to be very happy as they smiled at fans who waved at them both.
While Jude shares no kids with his current girlfriend, he is father to five children from other relationships.
The father-of-five shares Rudy, 16, Iris, 18, Rafferty, 22, with actress Sadie Frost, 53, from their six-year marriage.
In 2009 Jude became a father again for the fourth time when his daughter Sophia was born to model Samantha Burke.
Six years later he became a father again to Ada, three, with songwriter Catherine Harding.
For more details – click through the photos.
Law, 46, wrapped up from the cold in a brown double-breasted wool coat with a black scarf wrapped around his neck.
The pretty blonde wore a black jacket, turtleneck and scarf for the afternoon water trip.
She also sported a pair of fluffy earmuffs and chic shades for her ride.
Commenting on their relationship Law said: "And our relationship is a very private thing, and I think part of the fact it works so well is exactly because of that."
He added: "She's mine and no one else's. I'm very, very happy."
Law's girlfriend is a psychologist and she never talks about their relationship. The British actor is busy filming Paolo Sorrentino-directed series, 'The New Pope' for HBO.
We pay for juicy info! Do you have a story for RadarOnline.com? Email us at email@example.com, or call us at (866) ON-RADAR (667-2327) any time, day or night.