Nearly 2,000 feet deep into the Atlantic Ocean somewhere off the coast of Cape Eleuthera in the Bahamas, Thomas Pruim sat inside a tiny submarine with a ring in his pocket.He had a proposal planned that would make any woman swoon — especially if that woman was a biologist who loves marine life like his girlfriend, Christina Pilla.It was just a matter of getting the words out. The rest had fallen into place almost effortlessly. Pruim, a Tampa software developer, early this year entered an online contest hosted by Airbnb. Less than three months later, Pruim and Pilla were hovering above the ocean floor in an exploration vessel from the TV show Blue Planet spotting Cuban dogfish, white sea urchins and "wild-looking star fish." "I still can’t believe it all came together," said Pruim, 28. "You kind of always want to give someone the experience of a lifetime, especially someone who means so much to you."RELATED COVERAGE: As Airbnb’s competitors grow, Florida tax collectors work to strike more deals Pruim saw an ad online for the contest — part of a series that the home sharing app Airbnb runs to promote exotic locations — while taking a break from a late night of coding. Contests have included winning a few nights in a Lego house, Dracula’s castle in Transylvania or, in this case, aboard the Alucia with the crew of BBC’s marine exploration show Blue Planet II. It was 2:30 a.m. when Pruim typed up his entry letter:"My ideal deep sea adventure would be with my incredible girlfriend, Christina. I would go to the ends of the Earth with her, which is why I would want to see the ocean floor." MORE: Go here for more Business News He also mentioned that Pilla, 26, works with a consulting company to protect gopher tortoises and loves marine life.Pruim found out he won less than a month later. By the first week of April, the couple was on a plane to the Bahamas for a five-day trip. Pilla knew her boyfriend won the contest by writing an essay, but Pruim refused to tell her his entry’s content, keeping his epic proposal plans under wraps.When the big day came, he tucked the ring box into his pocket alongside a Tic Tac container in efforts to conceal the bulge. "She makes me smile every moment possible," Pruim told the Tampa Bay Times. "She really is one of a kind. There’s no other way to describe how awesome she is."The couple’s submarine dove to the ocean floor and started to make its way back up the seawall when Pruim decided it was time to ask the big question. They were at about 1,300 feet deep.He had one lined burned into his mind he knew he wanted to say: "While we’re on this adventure of a lifetime, why don’t we start an adventure for a lifetime?"He rehearsed it in his mind. And then, in the glow of under-water lights and cameras, it was time to finally ask."I’ve loved you every moment I’ve been with you," he told her before reciting his rehearsed line, and ending with "Christina, will you marry me?""Of course," she answered as she leaned over and gave Pruim a kiss. Then, it clicked for her. This was why he refused to tell he what he wrote in the essay."In the moment, I don’t even know if I can describe the feeling of it," she said. "Amazing is not even a good enough word for it." Contact Sara DiNatale at [email protected] Follow @sara_dinatale.