A 3m-wide creature swooping within inches of your face in the middle of a dark ocean probably isn't everyone's cup of tea.
But night snorkelling with giant manta rays off the Kona coast in Hawaii is undoubtedly a major drawcard for tourists.
I had the chance to get in the water with these creatures during a seven-night trip with Un-Cruise Adventures, which touts the activity as "thrilling" and an "unbelievable experience".
Lonely Planet says it is one of the top 10 activities on Hawaii's Big Island, and the Travel Channel voted it "one of the top 10 things to do in your life".
I had yet to be convinced.
A Kona Dive Company guide came on board to give us a quick lesson on manta rays and what we could expect from our hour in the water.
He made a few points that got me over the line and into the water:
One: manta rays are not stingrays and therefore do not have the eponymous weapon.
Two: manta rays do not have teeth.
Three: we were not supposed to kick around too much because it could scare them off. I assume it was not the guide's intention, but I liked that I now had a way to fight off these stingless, toothless monsters.
I shrugged into my wetsuit, and jumped into a skiff to be taken to the snorkelling site about 200m from the ship.
To attract the plankton and, in turn, the manta rays, divers put spotlights on the sea floor and snorkellers grip surfboards with torches pointing downwards.
Just that scene itself was amazing. About 100 people in full rubber suits and masks bobbing in the dark ocean with sharp lights coming up through the water was like something out of a science fiction movie.
We split into groups, six to a board, and lay still as the plankton gathered, wondering if the guide's "we see manta on 90 per cent of our outings" was going to apply to us.
It was quite clear when the first one appeared because fingers jutted out from all directions, everyone eager to point it out.
We got cooler as more arrived though, eventually just enjoying the experience and not feeling the need to alert each other to the new arrivals.
After 40 minutes of watching the rays cruise through the water, the winter Hawaiian waters had taken me to my limit and I climbed out shivering.
I agree, it was a thrilling, unbelievable experience - and I was also pretty stoked to have not been eaten.
Hawaiian Airlines flies direct between Auckland and Honolulu, with return Economy Class fares starting from $1235.
From there a domestic flight will get you to the Big Island.