There's plenty of diversity among the planets in the Solar System, hinting at an unimaginable diversity among the planets in our galaxy, not to mention the universe.
Mercury, the closest planet to the sun doesn't get as much attention as most of the other planets, but it's one of the most peculiar.
Because it's so close to the sun, Mercury has very long days, though very short years. It's not tidally locked, like the moon is to the Earth, so one day, i.e. one rotation around its axis, equals one year, i.e. one revolution around the sun, but it's very close.
Three days pass every two years on Mercury. One year is about 88 Earth days long and each Mercury day is 58.6 Earth days long.
This makes for some peculiar behavior and a very hot surface facing the sun. The video above describes this in more detail. Also interesting is how the sun moves in the Mercury sky because of this day/year cycle, as Universe Today points out.