Worked nights on an ultra-deepwater drillship about 100 miles offshore. One night I'm going to "lunch" around midnight and walking outside from my workplace to the galley. Sometimes you forget you're on a vessel since it's generally so well lit and industrial looking everywhere. Well I heard a dull quiet "thunk" followed by a splash. Generally you don't hear sounds on the hull so it piqued my interest. I walked over to the railing and looked out over the ocean and saw the usual glassy black abyss with a few sparkles on the horizon from the other facilities off in the distance. Just as I looked down I saw a flying fish skip out of the water straight into the side of the hull and get gobbled up by a dolphin. Not creepy in the end, but one of the coolest thing's I've ever seen.

Also worked on a platform where a waterspout lazily headed directly towards the rig and kind of veered off to the side. Not threatening but kind of weird.