Sentence:  Rich in Christian and Moslem art , Istanbul <WSD>is</WSD> today a fascinating museum of East and West that recently became a seaside resort as well with the development of new beaches on the Bosphorus and the Sea of Marmara only a short distance from the center of town . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)