The New Mosque (Yeni Cami), in Istanbul's Eminönü district on the Golden Horn at the southern end of Galata Bridge, is officially the Mosque of the Valide Sultan (Queen Mother) because it was commissioned by Safiye, mother of Sultan Mehmet III in 1597.

After her son died, Safiye was no longer Queen Mother, with a queen's powers and revenues, so her mosque sat unfinished.

Six sultans later, Turhan Hatice, Queen Mother of Sultan Mehmet IV, took up the work and finished it, which is another reason it's called the Vailde Sultan's Mosque.

I guess it is "new" because it was finished after Istanbul's other great imperial mosques: the Fatih Camii (Mosque of the Conqueror, 1470), Selimiye Camii (1522), Süleymaniye Camii (Mosque of Sultan Süleyman the Magnificent, 1557), and the Sultan Ahmet Camii (Blue Mosque, 1616).

But the New Mosque was begun before the Blue Mosque was. No doubt many of the workers who toiled on the Valide Sultan Camii were transferred to the Hippodrome in 1606 to begin work on the Blue Mosque. The Valide Sultan Camii was then finished by their descendants three generations later.

Inside is a wealth of gold, marble and faience (colored tiles). Be sure to take a look when you're in Istanbul.

Source: http://www.turkeytravelplanner.com