Returning to Future London

After finishing the story and saving after the credits, you are
returned to the Generator so you can continue exploring

Walk down to leave the Generator Room

Look at the map

Travel to the Surveillance Floor

Leave through the door on the right

Use the flying machine

Once you've landed back at the Thames Arms, you can use
the flying machine again if you want to return to the fortress

This free video game walkthrough is for the Nintendo DS
Professor Layton and the Unwound Future Walkthrough
Professor Layton and the Lost Future Walkthrough