"The Door To A Mystic Treasure" level: During gameplay, click the "Menu" option at the right side or display the "Options" menu from the main window. Pick the "Credits" option and wait until the list of developer names to reach the end. A block will scroll up from the bottom of the window. Drag and drop that block on the shoulders of the worker on the lower right side of the window that seems to be holding an invisible block. If done correctly, the message "Victory! The door to a Mystic Treasure has been opened. A new LOST WONDER is now available!" will appear. Click "Ok" to close the window and start the hidden level.
Extra time hint: After activating the "time freeze" bonus, keep using it once it is full and not near the end of the level. This will gave you a lot more time to complete a level.