[Geometry Dash] Glowstone Shrine was the first online level I played. It was a harder difficulty while I was pretty new to the game but I really wanted to end the first level before it expired (it was a daily level in GD World). After a lot of tries, a lot of effort and hours spent in of my phone screen, I managed to beat the level. It's the hardest online level I've ever beaten at the time of writing this.
Aside from my GD experience, I love this song!
Edit : Fixed some grammar. My hardest is now VVVVVV and my favourite level is now Pop Corn