You can probably start by checking the official website of the Boston Book Festival. There might be announcements about events related to 'one city one story' like reading groups or author talks.
It could be a program to promote unity within the city through a shared story. Maybe it encourages people in Boston to come together and engage with a particular piece of literature that represents the city's values or heritage.
Describe the city's layout. If it's a coastal city like Sydney, talk about how the city hugs the harbor. The Opera House might be a central feature, its white sails looking like they're about to set sail on the blue waters. Mention the beaches too, like Bondi Beach where surfers ride the waves and sun - seekers lounge on the golden sand. You can also include the sounds of the city, like the seagulls crying overhead and the distant sound of ferry horns.
The lost city of Za is probably not a true story. Such concepts often arise from folklore or are created for entertainment purposes. There's little to no concrete evidence to support its reality.