A City Of Crossroads
Samantha Peretore

Ayasofya (Hagia Sophia)
A no-brainer. Absolutely stunning. Make sure to see it lit up at night, too!
Süleymaniye Camii
AKA the Tiled Mosque. I think this is even more beautiful than the Blue Mosque, and it's a little more off the beaten path.
Suleymaniye Hammam
While in Istanbul, a visit to a Turkish Bath is a must! I should note that I didn't find the massage entirely relaxing - you're laying on hard marble, so having my ribcage and hip bones pressed into the slabs wasn't ideal - but it's a really interesting experience, and when they first cover you in soap, it feels like you're lying under a cloud (a super cool feeling). The Tellaks (male masseuses) have this down to a science, and work very quickly.
The Ortakoy area is worth an afternoon, and the Ortakoy Pier is beautiful. Stop by House Cafe for a drink and stop by a street cart for a stuffed baked potato - SO incredible.
360 İstanbul
Great drinks and 360 degree views of this beautiful city!
İstiklal Caddesi & Sidestreets
Istiklal Caddesi and the side streets off of it, especially toward the southern end of the street, are where you'll find all the young people, and it's amazing!
I would stay at: Hotel Ararat
This is more of a hostel than a hotel, but that's preferable to me at the moment. Tiny rooms, but reasonably priced, well located, and includes a great breakfast.