The Dark Side of the Moon.
I was about 12 or 13 in the mid-1980s when I bought a cassette copy of Dark Side for $2 at a garage sale. Only reason I bought it was because I'd seen the famous album cover on T-shirts and record shops for as long as I could remember and so I wanted to see what the big deal was.
First time I listened to Dark Side, I thought it was just plain fucking weird, LOL. On Side 1 I couldn't figure out which song was which because the tracks were all connected. I didn't like or dislike Dark Side the first time I listened to it, but the funny thing was I just couldn't stop listening to it -- and I have no idea why. It just seemed to resonate with me for some reason.
Jump ahead nearly 40 years and this is still one of my all-time favourite albums.