Final answer:
Irving sets 'The Adventure of the Mysterious Stranger' in a land of 'masks and gondolas' to symbolize the idea that appearances can be deceiving.
Step-by-step explanation:
Washington Irving sets 'The Adventure of the Mysterious Stranger' in a land of 'masks and gondolas' as a symbol of the idea that appearances can be deceiving. This is evident through the various characters in the story who wear 'masks' or veil their identities. For example, the main character Don Amador disguises himself as the Mysterious Stranger, highlighting the theme of deception and hidden identities.