For five long days, the envelope seemed to be staring Ms Kelly Bemmes down, daring her to peek.
Inside were the destination and itinerary for a weekend trip that the 22-year-old was taking with her mother, Ms Kim Bemmes.
It took some effort, but she resisted.
The mystery and anticipation was, after all, part of why the two booked the trip for US$650 (S$890) each via Pack Up + Go in the first place: The travel agency specialises in "surprise" vacations.
When her father dropped them off at Cincinnati/Northern Kentucky International Airport early on a Thursday morning in August, her mother did the honours. She opened the envelope and read where they were headed: Philadelphia.
Ms Bemmes said she decided to book the trip after reading about Pack Up + Go on Facebook. She had not travelled much and loved the idea of someone else planning her getaway.
She said that even though the trip was short, it was one of the best she has taken, because there was no stress involved. "I hate planning. Nobody wants to check for his flights and hotel online," she said.
"And I just liked the surprise because I knew it was going to be somewhere I had never been and I didn't really have anywhere in mind I would prefer to go."
Pack Up + Go is one of a handful of surprise vacation travel agencies that aims to add a suspenseful twist to trips.
It works like this: Travellers go online and fill out a survey, which asks questions about recent trips taken, upcoming trips planned, vacation preferences, hobbies and interests, among others.
They can opt for a road trip (starting at US$400 a person) or a flight, train or bus (starting at US$650 a person) and the travel team gets to work planning a three-day weekend in the United States shaped by the survey.
A week before the traveller embarks, the company sends an e-mail with a weather report and packing tips, such as whether to take along a bathing suit or hiking boots. The envelope with the destination, maps and confirmations arrives via mail.
Pack Up + Go founder and chief executive Lillian Rafson launched the business last year in Pittsburgh after first hearing about surprise vacations while travelling in Eastern Europe.
With Pack Up + Go, she decided to focus on planning trips in the US to encourage domestic travel.
"I was in Riga, Latvia, when I first heard of this, but at that point, I had never been to Charleston, South Carolina," she said.
The Vacation Hunt is an agency that adds an additional twist to the mystery vacation game: Travellers receive clues leading up to the trip.
Mr Jeff Allen and Ms Roshni Agarwal, the husband-and-wife team behind the Washington-based business, comb through books and sift through trivia to try to find clues that are challenging enough such that clients cannot just Google the answers and spoil the big reveal.
They decided to start the company after Ms Agarwal planned a surprise 30th birthday getaway for Mr Allen. She loved how the hints along the way built excitement for the trip and it was fun for them.
The Vacation Hunt's surprise vacation package (starting at US$750 a person in the US or US$950 a person internationally) includes flights, accommodation and at least two pre-planned activities.
Travellers receive two or three clues by e-mail. An envelope with the destination, confirmations and itineraries comes by mail a few days before the trip.
In Britain, a cruise company is about to launch its first luxury mystery cruise. The Secret Sailaway, by Bolsover Cruise Club, will embark on March 9 next year and sail to six cities over 16 nights (at just under US$16,000) from an undisclosed starting point.
To build suspense, riddles are available online for passengers to try to decipher. They can also request the answers after booking or they can await the big reveal as they sail into port.
Like the other leaders in the burgeoning surprise-vacation industry, Mr Michael Wilson, managing director of Bolsover Cruise Club, said the goal of the cruise is to add a little thrill to the adventure.
"It is a completely different way of seeing the world, simply taking a leap of faith and seeing where you end up," he said.
"The thought of arriving at the airport with no idea where you are heading until you check in is so exciting."
THE WASHINGTON POST