With domestic U.S. travel on a healthy upswing, Amtrak Vacations has rolled out 25 new rail vacation packages, bringing its total number of offerings to about 350.

The packages are independent and available most days, based on train schedules. The packages can be bought off the shelf, assembled and ready to go. But they can also be customized.

"There are more than 350 itineraries total, an infinite number of variations," said Frank Marini, president of Amtrak Vacations. "You can add, build, or change anything you want based on the customers' needs."

Amtrak operates in 46 of the 48 contiguous states (South Dakota and Wyoming are the exceptions). Packages can be built combining segments for practically any domestic location where people want to travel.

"You can start at any point you want, or end at any of 500 station points," Marini said. "We also connect in Canada with VIA Rail, so you can also add any of those points."

The centerpiece of the new batch of programs plays to the surging popularity of the national parks. It's called Grand National Parks. It's a round trip from Chicago by train, incorporating rides on three of Amtrak's most stylish trains, and it visits three of the most popular national parks - Yellowstone, Yosemite, and Grand Canyon.

The trip rides the California Zephyr from Chicago to San Francisco/Emeryville, the Coast Starlight from Emeryville to Los Angeles, and the Southwest Chief from Los Angeles to the Grand Canyon and back to Chicago.

The new programs were put together based on observing the buying preferences of customers.

"We watch what people are tailor-making, and when we see a trend, we create a package," Marini said. "We introduce new programs throughout the year, not just at official launch dates."

Amtrak Vacations is undergoing a surge in demand and an increase of sales volume, benefiting from a boom in domestic travel apparently based on a combination of factors.

Though the fear that was churned up over terrorist bombings this year is fading, travel to Europe has not returned to previous levels.

"Europe is still soft," Marini said. "Maybe the fact that it is an election year is contributing to it, but we are seeing a boom in domestic travel."

Domestic train travel and visits to national parks are booming, which adds up to a double jackpot for Amtrak Vacations. And the people buying are often, surprisingly, experienced world travelers.

"In the past, domestic travel hasn't been the sexy thing," Marini said. "It's been eclipsed by travel to Europe or the Middle East. But now, because of the decline in Europe, many of these travelers are looking at domestic travel. Our travelers have traveled the world, but they haven't seen their own backyard. They want to see it, but in different ways."

When you are traveling by train, it's not just transportation, Marini said. It's a whole experience: the historic rail experience. With no concerns about driving or traffic, you are free to focus on the scenery.

"People are looking for new experiences in the U.S.," Marini said. "Traveling by train is a whole other aspect. The train is part of the experience. I see it as the new river cruising."

As with river cruising, accommodations can be available aboard the train, and like river-cruise ports, rail stations tend to be centrally located.

"The East Glacier train station, for example, is only 208 steps from Glacier Park Lodge," Marini said.

Apparently, many people are making that discovery, as Amtrak is attracting many new customers. Sixty-three percent of Amtrak Vacations passengers are first-time customers.

Marini is trying to alert travel agents to the potential of domestic-rail vacations.

"I recently asked a group of agents how many sell cruises," Marini said. "Of course, many hands went up. Then I asked how many sell the U.S. national parks and rail vacations, and there were not as many hands.

"But I told them, according to [Cruise Lines International Association], 23 million people cruised globally in 2015. But in a calendar year, 31 million people travel on Amtrak. And last year, 307 million visited national parks. Cruises are great, but you want to make sure you are offering trains and national parks."

Marini wants to follow the lead of the cruise lines.

"Cruises make it easy," Marini said. "All the expenses are on the ship. We make it easy with our packaging."