Edirne

Edirne is a city in Eastern Thrace, in northwest Turkey. It lies on the gently rolling Thracian plains and just east of confluence of Maritsa, Tundzha, and Arda Rivers, known in Turkish as Meriç, Tunca, and Arda, respectively.
This city can be your first or last destination in Turkey, depending on the direction of your itinerary, since it’s located at the junction of the borders of three countries: Turkey, Greece, and Bulgaria. Visiting this city is also feasible as a long day trip from Istanbul.
This city is very old at the same time it has comprehensive cultural wealth.
Downtown, Main sights in downtown are quite close to the main square and to each other, and can be (hastily) done in half a day.

Selimiye Mosque, (Selimiye Camii), (at the central square). That mosque which dominates the skyline of the city, built on a slightly higher hill than its surroundings, although a play on dimensions makes the exterior sight of the building smaller as you get closer to it. A grandiose piece of art by Sinan, the Ottoman architect of 16th century, Selimiye is usually considered the zenith of Ottoman architecture and has been listed as a World Heritage site by UNESCO in 2011. 
Old Mosque (Eski Cami), (at the central square, across the street from Selimiye). The smallest—and the oldest—one of three nearby, imperial mosques in downtown Edirne, it's known for its calligraphic inscriptions on its interior walls with a small central dome atop.
Üç Şerefeli Mosque (Üç Şerefeli Cami), (just north of Old Mosque, close to Selimiye). This mosque is easily recognizable, having four distinctive minarets that all have very different designs, uncommon during the 15th century, one of which has three balconies, giving it its name which literally means "three balconied". Long undergoing restoration, interior of the mosque, which features a colourfully decorated central dome, smaller surrounding domes of varying sizes each featuring a different colour pattern, and very stately columns supporting them, has recently been re-opened to visits.
Museum of Archaeology, An original prehistoric dolmen moved from its original setting and a reconstructed Thracian hut—typical of those used by the ancient folk of the region—is among the displayed in the garden of the museum. 
Museum of Islamic Arts (İslam Eserleri Müzesi), (behind Selimiye). A subsection of Museum of Archaeology. 
Old quarter. Locally named Kaleiçi,"walled city", this is the oldest part of the city although the city walls and gates have vanished a long time ago. Built in a grid plan after it suffered from a big fire in late 19th century, the main artery of this part is Maarif Caddesi, which lies two blocks west of Saraçlar Caddesi. Along the side streets and Maarif itself line a number of eloborate wooden houses, the walls of which are with highly delicate handwork, though some are derelict. At one end of the street is the Jewish Synagogue, the biggest one in Turkey and the whole Balkans, but is slowly decaying now.