Just down the hill from the famous Hagia Sophia Mosque, near the shores of the Sea of Marmara, stands Istanbul's oldest surviving Byzantine monument. We literally stumbled upon Little Hagia Sophia at the end of a dead-end street, thought it was closed due to heavy drapings over its doors and were about to turn and leave the grounds when several people emerged from inside and around the door covering...so we entered. From its intricately-designed dome to the two-story marble colonnades, what an awesome sight! The mosque was entirely open to access, so we were able to climb the stairs to the galleries to fully appreciate the interior. We later found out from friends who live in Istanbul that Little Hagia Sophia is frequently not open to visitors, so we were indeed fortunate. A must see if possible.