Explanation: The correct answer is option B, Kolkata.

Kolkata is often referred to as the "City of Castles" because of the large number of colonial-era buildings and palaces that can be found throughout the city. These structures were built during the British Raj and reflect the architectural styles of the time. Some notable examples of these castles include the Victoria Memorial, St. Paul's Cathedral, and the Marble Palace.

Option A, Hyderabad, is known as the "City of Pearls" due to its historic role in the pearl trade.

Option C, Jaipur, is known as the "Pink City" due to the pink color of many of its buildings.

Option D, Delhi, is known as the "City of Djinns" due to its association with supernatural beings in Islamic mythology.