Watch, Listen, Visit
Sometimes I think people think (because I sometimes think) that the dark side of the moon is always the same - the side we can't see from Earth.
With just a little wobble, basically the same "side" of the moon is always facing the Earth. That's why you can almost always see the Man in the Moon or part of him.
But the dark side is always changing. The part of the moon that's in the shadow compared to the location of the sun is always changing. That's why you see the different phases of the moon - full moon, quarter moons, gibbous moons, and new moon - which you usually can't see at all, unless there's a good amount of earthshine to light it up.
You know what moonshine is, besides the stuff you drink. It's the sunlight reflected off the moon and to your eyes.
Earthshine is sunlight reflected off the earth and onto the moon. Sometimes, especially in winter when there's a lot of reflective snow, there's enough earthshine lighting up the moon's dark side that it becomes bright enough for us to see it back here on Earth.
To celebrate Dark Side of the Moon Day, you can watch that dark side whether it's lit up enough or not. You can listen to the Pink Floyd version of it. Or you can visit it, if not in person, then vicariously through some good science fiction books or movies.