You can see its incredible magnificent shape from Itsukusima Shrine, Machya-dori olden street and of course from the ferry boat. This five storied pagoda is definitely worth visiting.
You can appreciate a traditional wooden construction style of Japan. 

It was constructed in 1407, and restored twice, in 1533 and 1945. This pagoda was designated as an important cultural property in 1900 and belongs to Itsukushima Shrine now a days.

The origin of the five storied pagoda was the stupa, Buddha’s mound shaped grave in India, and it was introduced to Japan in the 6th century via China and Korea. The shape changed from a soil mound to a wooden building in China, then it evolved into the Japanese style.

There exist 22 five storied pagodas, designated as national treasures or important cultural properties in Japan.

After Buddhism was introduced, the central government troped to bring peace and prosperity through Buddhism, and encouraged local governments to build five storied pagodas with temples.

Emperor Suiko made Buddhism a state religion, and constructed a Buddhism based political system. So it was more a symbol of authority than a pure religion, I think.

Having five roofs refrects from the Buddhist world view.
A view of the world of Buddhism is represented by the five biggest elements: the earth, the water, the fire, the wind, and the sky, and these five roofs have this meaning.

At the time of Meiji Restoration, Meiji government ordered Shintoism and Buddhism to separate. Miyajima’s five storied pagoda was dedicated to Yakushi Buddha, Fugen Bodhisattva, and Monjyu Bodhisattva statues , but they were moved to the Daiganji temple.