Hardest Led Zeppelin Riff To Play On Guitar? It's Not What You Think....

This is the hardest Led Zeppelin riff for me to play on guitar, and I've been playing guitar for over 40 years. It's from a song from the Led Zeppelin 3 album, 1970. I find the picking to be really tricky. Do you have trouble playing this riff? What's the hardest Led Zeppelin or Jimmy Page riff for you as a guitar player?