MrBeast and his friends spending seven days exploring a massive underground city, which is actually a thousand-year-old salt mine. Throughout their stay, various famous YouTubers join them daily, leading to escalating chaos and humorous situations. They explore hidden tunnels, find secret chambers, set up a base camp, play games, and even experience a short-lived "dictatorship" within their underground community. The challenge culminates in a final day of reflection and their eventual return to the surface.