"A few days before, he had given me a rose and asked me out on a date for the next night," Jessa, 21, told PEOPLE Magazine.
It was a triple date with both sets of parents, which surprised Jessa because she had no idea the Seewalds were in town. Before the night was over, Ben gave Jessa a box containing an iPad with a video message that he had recorded, saying: "This is the first clue to the rest of your life."
"I had done a few things to throw her off track," Seewald told PEOPLE. "Jessa is really good at figuring things out and I wanted to surprise her."
The scavenger hunt, which Ben said took him months to plan, began with a plane ride with pilot John-David Duggar from the Duggars' hometown of Springdale, Arkansas, to Eureka Springs, Arkansas. Jinger Duggar accompanied Jessa.
Throughout the day, Jessa had to get a hole-in-one at a miniature golf course, collect a dozen roses from strangers in a park, take a trolley tour while filling out a quiz, and ride in a train with other members of her family. The final clue led her to Thorncrown Chapel.
"I walked in, and he was standing there at the front," Jessa told PEOPLE. "I could barely talk. I knew he was going to propose. I cried."
Ben got down on one knee and presented a .75-carat princess-cut diamond engagement ring.
Both the Duggars and the Seewalds are overjoyed.
"Michael and I could not be more thrilled for Ben and Jessa," Ben's mom, Guinn, told PEOPLE. "Having similar goals and interests, they balance and complement one another beautifully. We praise God for the blessing of this relationship between Ben and Jessa."
Following Duggar tradition, Ben had to ask Jim Bob's permission to marry Jessa. The Duggar dad was "100 percent on board" and gave Ben his blessing, along with Michelle's
If Jessa and Ben take the same route as Jill and Derick, they will have a short engagement. Jessa said that, like Jill, she wants to keep her wedding cost effective so she can splurge on the honeymoon.