Dan Nguyen and his wife Olivia Nguyen run a popular Instagram account @spongecake_thescottishfold, which has over 314,000 followers, as well as the TikTok page @spongecake_cats, which has 199,000 followers as of Friday.

Both document their three cats as they explore the world — Venice, Paris, Milan, and more — from the comfort of Dan's travel backpack.

Olivia started the social-media accounts in November 2021, as the family embarked on their first international trip to Paris. The second video she posted in November showed Dan hugging Sponge Cake with a view of the Eiffel Tower in the background. The video received over 192,200 views and 16,900 likes. 

Speaking to Insider, Dan said he and Olivia got Sponge Cake and Mocha, two Scottish Fold cats, and Donut, a British Shorthair, in the summer of 2020. With gradual training, the indoor cats — who Dan calls his "pandemic babies" — have grown accustomed to the outside world, according to their owners.

Dan said Sponge Cake is "a very adventurous guy who likes to explore" and is "very attached" to him and Olivia, whereas Mocha is "a very sweet boy who is always calm" and enjoys walks on Fifth Avenue. Last but not least there is Donut, the last cat to join the family. Dan told Insider that Donut was hesitant to go outside at first but is now the biggest fan of the outdoors.

Olivia started social-media accounts for their cat trio just as Dan started training them for travel by taking them to local destinations like Central Park. Over time, their trips became more adventurous and their online following grew.

According to Dan, who wrote "Adventure Cats: How to Train Your Cat for Outdoor Adventures," a book published in July outlining his process of training indoor cats to go outside, it's best to teach them "incrementally" with a lot of treats, gentle petting, and encouragement.

To those hoping to emulate Dan and Olivia's success, their advice is to get your cat to trust you and feel safe with you.

Their first out-of-state adventure was a trip through Orlando, San Francisco, and Sacramento in 2021, Dan said. Dan's reason for bringing the cats was simple: "We wanted them to be with us." 

The trip gave them the confidence to go abroad for the first time that November to Paris, which Dan said the cats particularly enjoyed. 

Since then, they've gone on to explore Venice and Milan, and Dan said they are aiming to visit Switzerland in the fall.

But taking Sponge Cake, Mocha, and Donut abroad is no walk in the park as most countries have different rules about traveling with cats, he said.

Dan said getting certifications from their vet for certain airlines was helpful, and much faster than the lengthy process of getting certified by the US Food and Drug Administration.

This meant he and Olivia could simply check in with the vet to make sure their pets are safe to fly and have the correct vaccinations prior to traveling. If you plan on traveling with your pet, you can search for your destination on the United States Department of Agriculture's website to find the most up-to-date requirements.

Dan and Olivia prefer not to put their cats in the hold when flying, instead opting to take them into the cabin with them. For pets that weigh under 10 kg, or around 22 pounds, Dan says you can take them in carriers that qualify as hand luggage and fit them under the seat in front of you. He added that the cats sleep in their carriers whenever they are tired during long flights.

As Sponge Cake, Mocha, and Donut outnumber their parents, sometimes Dan and Olivia need to book an extra ticket, but not all airlines allow them to do this. "At times, when I wanted to buy a third ticket and an empty passenger seat, it's not allowed," Dan told Insider, noting that they only allowed one pet per human passenger and wouldn't allow them to buy a ticket for an empty seat. 

The day before a flight, the couple also sets aside one full check-in suitcase for the cats. "In it is disposable litter boxes and a little bit of litter, wet and dry food, and then all their toys, and scratching posts," Dan said, adding that he and Olivia always try to re-create their home environment at the destination. 

"We get a lot of laughs, a lot of smiles, and a lot of curiosity. We get a lot of people coming up to us and wanting to say hello to them, which is always fun," Dan said, noting that people often ask how he got the cats to be so comfortable outside in busy spaces.

Back home in New York City, Dan said the cats often enjoy spending time in Central Park or Times Square, or outdoor dining with their parents. He added that he and Olivia are wary of not overwhelming their pets with attention from passersby but cat lovers will still come up to them and take photos.

Olivia makes the cats' custom bow ties and also purchases knitted pastel sweaters for them to wear.

"All the bow ties and the ribbons that you see are custom-made by my wife," Dan said, noting that Olivia dresses them up for "fun and photos." 

He added that Olivia's designs are fragile and need special treatment when they travel. "She actually does not put the bow ties and stuff into the suitcase because they're too valuable to her and they're so delicate, so she actually carries them on hand in a box," Dan said, laughing. 

A few things Dan said he has learned about traveling with cats include just how long it takes for them to pass security checks, which can be extra difficult if they aren't comfortable with the process. He also said it's important to research pet-friendly hotels in your destination and to do extra planning to create a pet-inclusive itinerary.

While the Nguyens have never lost track of their cats, Dan said it can be a challenge when they climb trees. One of his best tips for those bringing their cats to urban spaces is to not let them climb higher than you can reach, he said.

"Sometimes, one of them goes too high," Dan said. "Then we have to gently wait them out. I put my backpack with the top down and I hold it up to them and eventually, they'll jump into the backpack." 

After boating in Lake Como and prancing outside Paris' Louvre Museum, it's safe to say no limit to how far these cats will go.