Pearl Jam are celebrating 20 years of rocking our world with a two-day festival that's currently shaking the rafters at the Alpine Valley Music Theater in Wisconsin. At last night's kickoff, PJ played a rarities-heavy three-hour set, according to Billboard, which no doubt delighted the band's bootleg happy/collector mindset fanbase. However, the highlight of the set was when Soundgarden vocalist Chris Cornell joined Eddie Vedder and co. onstage to perform three Temple of the Dog songs and a Mother Love Bone track. It was a grunge revival if there ever was one, as Temple of the Dog were essentially PJ with Chris Cornell as the main vocalist, and the mini-set took place during the second encore.

Their rendition of 'Hunger Strike,' which was a radio hit in the 1990s, was simply captivating, as the video below demonstrates. Cornell was able to strike a real 'Jesus Chris Pose' with his long hair, which was the siren-like singer's signature look during Soundgarden's heyday. Anyone who grew up in the grunge area will appreciate any and all YouTube footage of this song being performed, given the rarity of the occurrence. It was powerful enough to teleport fans to the early '90s, as Vedder's and Cornell's voices have held up after all these years and they belted out the song with the virility of young men.

Other Temple of the Dog songs played by the band included 'Say Hello 2 Heaven' and 'Reach Down,' as well as 'Stardog Champion,' which was a Mother Love Bone song. Grunge fanatics already know that Temple of the Dog was conceived by Cornell as a tribute to the late Andrew Wood, the singer of proto grunge band Mother Love Bone, which also featured PJ bassist Jeff Ament and guitarist Stone Gossard.

Mudhoney also hit the stage to join the band for a cover of MC5's 'Kick Out the Jams,' while the Strokes' vocalist Julian Casablancas lent his pipes to PJ's 'Not For You.' He was repaying the favor that Vedder did the Strokes, by guesting on the band's 'Juicebox' during their set. Queens of the Stone age leader Josh Homme showed up for 'In the Moonlight,' which was quite the surprise.

Additionally, Pearl Jam's rhythm section -- Ament and drummer Matt Cameron -- and guitarist Mike McCready performed with Joseph Arthur during his set on the fest. They performed two songs from the forthcoming debut album featuring all four musicians. There is no title or release date for that disc yet.

Vedder addressed the band's 20 years of rich rock history, saying, "It's hard to imagine. When you're a kid, you think that music is the most powerful thing in the universe [but] adults around you being practical say that [success in a band] ain't gonna happen. Get a nice construction job. We didn't listen. I want to thank the kid I was for hanging onto his passion."

Watch 'Hunger Strike' from the Pearl Jam Fest