Ali Qapu (lit: "Grand Gate") is an imperial palace in Isfahan, Iran. It is located on the western side of the Naqsh-e Jahan Square, opposite to the Sheikh Lotfollah Mosque, and had been originally designed as a vast portal entrance to the grand palace which stretched from Naqsh-e Jahan Square to Chaharbagh Boulevard. UNESCO inscribed the Palace and the Square as a World Heritage Site due to their cultural and historical importance. The palace is forty-eight meters high and there are six floors, each accessible by a difficult spiral staircase. In the sixth floor, Music Hall, deep circular niches are found in the walls, having not only aesthetic value, but also acoustic. Ali Qapu is regarded as the best example of Safavid architecture and a symbol of Iran's Islamic heritage.