Describe one of the strangest thing you have ever seen or experienced?

I don't really know if you mean paranormal experiences or something else, but here I go:

Not too long ago I was walking around in my high school to get to one of my after school clubs. Not a lot of people were there because most student leave right after school unless they have a club meeting and the staff would usually leave on time, too. But as I was saying, I was walking around and I heard giggling. At first, I thought it was just a student walking to their club. But I kept hearing it while walking while no one was there. Then I started to hear footsteps. Still no one around me. At all. I was starting to get paranoid so I started to speed walk to the club room. Mind you, the high school I go to is very big. I was almost to my destination when I saw a figure out of the figure of my eye. When I turned to look at it, it was gone. It still gives me chills.

My ex friend said her mom had seen aliens before, I didn't believe her so I asked her mom and she said it was true