For ten points, name this structure built on an island off the coast of Egypt.
It was first described in the tenth century CE by Idrisi and Yusuf Ibn al- Shaikh. Its lowest level was a square 56 meters high with a cylindrical core, while its middle level was octagonal and the third level was circular. Its total height, including the foundation base, was about 117 meters and the internal core was used as a shaft to lift fuel. In 1480 Qaitbay used its ruins to build a fort. In November 1996, divers claimed to have found some of its remains, including the name of its designer hidden in the foundation. Created by Sostrates of Knidos, it was finally completed during the reign of Ptolemy II. For ten points, name this structure built on an island off the coast of Egypt.
It was first described in the tenth century CE by Idrisi and Yusuf Ibn al- Shaikh.
{Lighthouse} at {Alexandria} (or {Pharos} of {Alexandria}, but make sure they say Alexandria)