Next to the Beautiful Door, there is a baptistery with a small narthex and a holy well which has been closed.
The baptistery was used as a storage room of lamp oil during the Ottoman Era and later was turned into a mausoleum of Sultan Mustafa I & Sultan Ibrahim. There are still terra cotta oil lamppost inside the small building.
The marble baptism crib in the baptistery was uncovered when Hagia Sophia turned into a museum and is now on display. The crib was believed to have a healing power.
In his ‘’A Desription of Hagia Sophia’’, Paul Silentiary describes it: ‘’ Following these four graceful Thessalian columns, on either side, namely towards dusk and dawn, pierced cylindrical vaults are poised on the divinely built walls along the length of the aisle and serve for passage. Towards the north wind they open into double doors, whereas towards the south, over against the doors, are well-wrought spaces like chambers.’’