The lowest elevation I've ever been to is Death Valley National Park in California, which gets down to 282 feet (86 m) below sea level. It's particularly crazy because a few hours drive away we saw Mt Whitney, the highest point in the continental USA at 14505 feet (4421 m).
Beyond that, I have an open water diving certificate so I think the lowest with that was ~50ft or so (16m). And of course now that I'm in Holland I permanently live a few meters below sea level.


