Final answer:
St. John's is the capital and largest city on the island of Antigua, known for the prominent St. John's Cathedral, a significant baroque architectural landmark and tourist attraction.
Step-by-step explanation:
The capital and largest city on the island of Antigua, which houses the namesake Cathedral and is known as a main landmark, is St. John's. St. John's Cathedral, also known as St. John the Divine or the St. John's Cathedral, stands out as an example of baroque architecture and is a significant attraction for visitors to the island. Similar to many cathedrals in Latin America and the Caribbean, these religious structures are not only places of worship but also serve as important historical and cultural symbols. Tourism, including sightseeing of renowned cathedrals and landmarks, is vital for the economic development of Caribbean islands such as Antigua, leveraging the beauty and historical importance of these sites to attract visitors.