Writing a caption is simple. All you need are the six Ws who, what, where, when, why and how (OK so the w in how is at the end).
Tourists can visit the Qolşärif mosque in the Kremlin of the Russian Federation city of Kazan opened in 2005. It is built on the site of a previous mosque that was established in the 16th century and destroyed when Ivan the Terrible conquered Kazan in 1552
The caption under the photograph of the Qosarif mosque in Kazan uses most of these but if you click on the picture you will see a different version.
Why Different Versions?
If you are producing a general caption for a picture, e.g. an image that is being sold by a stock agency then include as much information as possible. An editor can always remove surplus information but it is difficult to add.
If you have a specific market or publication in mind then tailor your caption to that audience.