Because it was turned into a museum by the Ataturks in the early 20th century, the Hagia Sophia is no longer a place of prayer; which is good in that you are allowed to stand below the truly awe-inspiring central dome in slack-jawed amazement all day if you'd like to. Then again, hearing the evening prayer sung live from the minarets of the Blue Mosque is the type of experience that will give you chills. Depending on the time you have available, you may choose to enjoy the Byzantine mosaics in the upper reaches (which tops out at 56 meters/184 feet in total height), the intricate original stonework, and the overall grandeur of Hagia Sophia and then, by all means, take the less-than-ten minute walk to the Blue Mosque to make a day of Istanbul's peerless religious sites.
Tickets will cost about $15 USD and guides may be hired at the entrance. For more on this truly must-see world landmark, browse our included links.