Instructions
Walk down the stone path and enter the building. Avoid getting squished by the columns in the building by running through them when they're up. When you reach the last column, go into the hole underneath it. Follow this path, beating up the cyclops and his minions along the way.
Use the cage to climb up onto the ledge where the cyclops was. Stomp on the switch to open the gate, then walk through it.
Walk along the path until a guard comes and locks you in with a bunch of prisoners. Once locked up, use your fairy dust attack to get the guard to come and open the door, then continue along the path.
Cross the platforms without falling down, then turn to your left. You'll come up to a set of stairs -- ignore these, instead choosing to float into the hole. At the bottom you'll see Fiona. Use your fairy dust attack to open the gate. Note at this point that you'll take control of Fiona.
Use Fiona's fairy dust attack on the door to get it to open. Smack the statue of the Fairy Godmother to get some extra fairy dust. Go into the next room where you'll fight some guards. To stop the guards, you'll need to use Fiona's fairy dust attack to move the stone blocks onto the switches.
You'll come across three switches. Hit the left one twice, then hit the right one, and the door will open. You're free from the prison detention center.