So, the problem of musicians for the festival has been solved, but Pauline has another problem on her hands. To get to the underground power plant, you will need to find the big manhole cover, which is in a spot you might know if you used that parked taxi to get to the last musician. If you didn’t, then it’s literally right next to the Outdoor Cafe flag. Capture the manhole cover, move it and enter the underground power plant. The first area has nothing of value, so just follow the path around and enter the pipe at the end.
The next area will have some Poison Piranha Plants, as well as some platforms that spin around when you hit them. Make your way past the first two spinning platforms to the third area. Take care of the Piranha Plant and Stingbys, then look for a small ledge off the area to find three purple coins (55) . Backflip up to the double spinning platform and use your hat to gather the four purple coins in the air off to the one side (59) . Drop back down and make both platforms spin, then use them to get to the next ledge, where more Stingbys await.
For the last bit in this room, shoot your cap at the contraption, which will hit the vertical spinning platform. Get on the platform, but you will want to move to the top of it, as there will be a ledge off to the one side that leads to a Power Moon (Sewer Treasure) . Use the pipe at the end to reach a room, where Pauline will be waiting for you, along with two large Piranha Plants. Being mindful of the poison on the ground, stomp the Piranha Plants to make a Power Moon appear (Powering Up the Station) . The glass covering the switch at the top is now broken, so ground pound the switch to power up the city, which will trigger the start of the festival.