I will be traveling north in a week, around the area of the greek Thrace and will be crossing the border to the east in turkish Thrace, maybe going over to Istanbul.
What's interesting around there to visit and explore (apart from Istanbul which I know)?
If anyone wants to also meet, even better!

Edirne is probably a bit north of where you're going, but it has some wonderful architecture, including one of Sinan's finest mosques.

Edirne: the Selimiye mosque and Old mosque are well worth a visit. If you are travelling with your own vehicle try the route between Sarkoy and Tekirdag, along the Marmara sea. This road passes through some picturesque villages (e.g. Ucmakdere) but may become unusable in bad weather. Travelling around the Istranca mountains in the north is a bit more time consuming but will again take you through small hamlets where you can stop by the coffeehouse and have a chat with the village elders:) Apart from some of the architecture in Edirne I don't think Thrace offers huge spectacles, but there is a lot of potential for people/reportage photography in the smaller places.
Also, if you can make it in June/July one day, there is the famous 650 year old wrestling event in Kirkpinar.
If you do make it to Istanbul, I'd be happy to meet.

Thank you for all the information!
I am going to see the gf, so everything's up to her really and there is no set plan yet.
We'll see how it goes.