Calm, peaceful, and untroubled.
“The lake looks serene with no ripples on the water.”
“It's a serene setting, with only a few people quietly reading in the park.”
Use this word to describe quiet, peaceful scenes such as a lake, garden, or empty park in Task 3 — it's a strong descriptive adjective that contrasts well with 'bustling' and shows you can match your vocabulary to the mood of the picture.
Synonyms: peaceful, calm, tranquil