Mario & Luigi: Superstar Saga/TeeHee Valley, Little Fungitown and Guffawha Ruins

TeeHee Valley
After you battled Mom Piranha, you'll talk to Lady Lima and you'll see Peach Arrive. Afterwards, you'll transition to Beanbean Castle, and after a scene, you'll get told to go to TeeHee Valley in order to arrive to Little Fungitown (You need to head back to the Queen's throne to trigger that dialogue)

Getting the Super Hammers (And Secret Scroll 1)
After getting out of the castle, the Hammerhead bros will tell you about their new shop settlement. You actually need to go here in order to get to TeeHee Valley. Head to the eastern exit of the town, and then from the room you exit to, head upwards. In that room, you'll see an orb. Use Luigi in order to activate it, and open the steel gate. Follow the tree path all the way to a cave. Use the stairs to go down and you'll get to them.

After getting the hammers, head back to the area with the steel gate you opened, and head upwards. You'll see a rock blocking your path. You can now break it with the Super Hammer. Here you'll see Peach and Toadsworth. You'll auto get to the next room along Peach, but Toadsworth will interrupt you, making Peach vulnerable, and she gets kidnapped. Head to the yellow pipe, drop down to the underground, and head left to get to the room in which Peach is in. (This is the same for every time Peach gets kidnapped in this area)