Sometimes, venturing down into the depths of the ocean can be a disturbing experience, as well as a serene one.
That was perfectly demonstrated by an expedition a few years ago that aimed to get to the very bottom of the so-called Great Blue Hole in Belize.
This flooded sinkhole is around 300 meters (984ft) across, and 125 meters (410ft) deep, making it one of the largest sinkholes on Earth.
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Of course, in the scale of the ocean that's barely a ditch, but it's deep enough that recreational scuba divers can't reach the bottom, or certainly shouldn't try.
So, in 2018 it was a submarine from Aquatica Submarines that managed to get to the very bottom, to see what was down there.
Contrary to any optimistic expectations, as the crew got down past the 90-meter mark the amount of marine life started to dwindle down to pretty much nothing.
By the time they got to the sea floor, this was almost zero, thanks to a toxic underwater layer of hydrogen sulphide across the sinkhole which stopped oxygen from getting to its lowest levels.
Erika Bergman, who was on the expedition, explained that it was a little like a graveyard down there, telling Business Insider: "We found conchs and conch shells and hermit crabs that had fallen into the hole and suffocated."
So, the sinkhole is almost a sort of trap for underwater life, and if they're unlucky enough to fall into it without being able to swim hard enough to escape, there's no getting away from a sticky end.
Sadly, though, it wasn't just marine life that was discovered post-mortem, but also the bodies of two divers who had died on a previous expedition at some point.
Bergman said: "We found the resting place of a couple of folks, and we very respectfully let the Belize government know where we found them. Everyone decided that we would just not attempt any recovery. It’s very dark and peaceful down there, just kind of let them stay."
That sounds like a fairly harrowing discovery to happen upon when you're trawling the depths of a sinkhole like this.
That wasn't the only human activity discovered, though, because Bergman also talked about how the team found bits of litter down at the bottom of the sinkhole, including empty soda bottles.
So, even if you head to the bottom of a toxic sinkhole that can't support any life, you still find human garbage, which is a pretty depressing thought.