Maybe Bryan Cranston and his wife should’ve run out of steam sooner.

After the couple got married in 1989, they tried to make the most of their honeymoon by having sex on the train that was transporting them from Switzerland to Italy. Prior to boarding, however, their travel agent clued them in on a fun fact about the ride.

“The travel agent said, ‘By the way, the third tunnel is 50 minutes long. It’s tradition for honeymooners to take advantage of that time’,” Cranston recalled on “Conan” Thursday. “I said, ‘Capiche.’ We’re doing this, much to my wife’s chagrin. I said, ‘Are you ready to use up seven calories?'”

The train Cranston and wife Robin Dearden took carried not only passengers but also their cars, so the famous couple remained in their vehicle the whole time — surrounded by other cars with families in them. When the train entered the third tunnel, it was as dark as the travel agent had described.

“It was an absence of light,” Cranston recalled. “You couldn’t see your hand in front of your face … It was exciting.”

Unfortunately, the couple’s X-rated activities didn’t pan out as planned.

“All of a sudden within a short period of time I start seeing the features of my beautiful wife’s face, and I’m thinking my eyes are getting acclimated to this,” Cranston shared, before adding that the train entered “broad daylight” while they were both completely naked.

“The children in front are turning around and their grandmother’s like, ‘No no no no.’ She gives me a look like, ‘You! How? No!'” he said.

He ended his horror story by revealing his wife’s reaction.

“My gorgeous wife says to me those three words you always want to hear: ‘Get off me’.”

This article originally appeared in Page Six.