Viall and Grimaldi, a 29-year-old special education teacher from Montreal, Quebec, Canada, first enjoyed an astronaut's experience on a zero-gravity plane in which they floated together and kissed in mid-air.
"My date with Vanessa was easily one of the coolest moments of my life. Zero G is such a surreal experience, and something that is a once-in-a-lifetime opportunity. The sensation of flying at zero gravity was unbelievable; it really was like we were floating in space," Viall wrote in his People blog.
"We were doing flips, eating floating water and crawling on the ceiling. Vanessa told me once we took off that she tends to get motion sickness, but for the longest time she was doing great! It wasn't until the last 10 minutes the barf baggy had to come out."
Grimaldi was horrified she was throwing up in front of Viall on their first real date, but the Bachelor comforted and assured her that there was no one else he'd rather share that adventure with.
"She was such a trooper -- getting a little sick didn't ruin the moment one bit. If anything, I couldn't help feel closer to her. I remember seeing her get sick and just wanting to do anything to make her feel better. I almost forgot where we were, I just wanted to hold her," Viall revealed.
The 36-year-old former software salesman said he went into their dinner that night on "such a high."
"I was excited to spend more time with Vanessa in the hopes that we could build on the magic that we experienced earlier in the day. Sitting down with Vanessa, we connected so easily. Talking about family, relationships and what we want in our futures. The chemistry between us intensified," Viall said.
"I'd always found her beautiful, but our emotional connection took hold."
Viall actually cried on his date with Grimaldi because he had such a wonderful day with her. From a viewer's perspective, it was the first time Viall gave himself fully to the process and became optimistic about finding mutual love through this crazy process. (He was ready to propose to both Andi Dorfman and Kaitlyn Bristowe on The Bachelorette but finished as the heartbroken runner-up both times).
"I didn't expect to get emotional around Vanessa and thinking back to that moment, it was because I felt an incredible sense of excitement, and hope. Starting this journey, I was stressed this wouldn't work out. Not because there weren't amazing women, but I just know how rare it is to find a lifelong love," Viall explained.
"I feel like I had put a lot of pressure on myself to be the best, or be the man every one of the women wanted me to be. But in that moment with Vanessa, it was clear, that if a connection like this could happen this early, then this whole thing could lead to finding the one."
It sounds like Viall's date with Grimaldi was a total turning point on this season of the ABC series.
"I walked away from that night with a new sense of confidence not only in myself, but in this journey -- and Vanessa was a woman I would be lucky to have as a partner," Viall admitted.
Grimaldi, however, later confronted Viall about his sexual behavior with The Bachelor villain Corinne Olympios. Could the dynamic of their special romance change as a result?
"Next week you'll see how things go down with Vanessa and I, as well as the rest of the women. I know the decisions I make can't please everyone," Viall teased.