Hagia Irene means "Divine Peace" in Greek, so it was a church dedicated to holly peace, not to a Saint Irene as it's wrongly pronounced today. It's beleived that the church was first built in the 4th century AD over the ruins of a pagan temple by the Byzantine Emperor Constantine I. The wooden construction was burned during the Nika Riot in 532 AD and it was renovated by Justinian I, rapresenting typical characteristics of early Byzantine architecture. During the following centuries the church was restored several times because of the earthquakes and some big fires.
The Janissaries used the church as an arsenal after the Conquest of Constantinople in 1453. The staircases to the galleries and the inscription on the gate was added by the Ottomans. In the 19th century it was opened as a sort of museum displaying old weapons. At the beginning of the 20th century it was closed and remained empty for many years, until they started the restorations.
Today, Hagia Irene church is located in the first courtyard of the Topkapi Palace behind Hagia Sophia, and is called as Aya Irini in Turkish. At present, some classic music concerts or art exhibitions are organized in the building during important festivals. It is a museum today but it requires a special permission to visit it on regular days. Inside, nothing much remained from its original mosaics but a large cross above its main narthex, showing us that they were never re-made after the Iconoclastic period.
Hope to see you soon in Istanbul.