1582
Sea Level
(imgs.xkcd.com)
Alt text: They're up there with coral islands, lightning, and caterpillars turning into butterflies.
Tidal currents are the least outlandish phenomenon. Most planets have moons and those that do all have tides. Most known ones don't have oceans and land.
That being said the tides tend to be stronger in e.g. the north sea as opposed to the Mediterranean.