UK to Istanbul

So I'm taking a year off work and in August setting off on a 2 or 3 month cycle tour to Istanbul (and maybe back?)

I've got a vague route planned for the start, as I'm staying with friends in Brugge, Rotterdam, Utrecht, then down to Koln. After that I'm not so sure, probably heading vaguely in the direction of Stuttgart, then Munich, and pick up the Eurovelo route along the Danube to Budapest.

After Budapest I'm not sure whether to head through Serbia into Bulgaria and then onto Turkey, or Romania -> Bulgaria -> Turkey.

Has anyone got any experience of some or all of this route? Any tips or suggestions? All advice welcome!

So far my only cycle touring experience was from St. Malo to Bilbao last summer, where I met up with @Gustav en route as he was doing similar.

If anyone is doing something similar this year then let me know, as it'd be good to have some company part of the way.

The first couple of transcontinental races went from U.K. / Belgium to Istanbul. Few routes online that may be of interest?

We went by train from Zurich to Istanbul, via Austria/Hungary/Romania/Bulgaria/Turkey, except a couple of days in Romania when we travelled with local guides in their cars - the traffic is probably not heavy in the countryside, but the driving on A-road equivalents was petrifying!

Istanbul was the real standout part of the trip and I would definitely recommend allowing a few days (at least a week) to explore it.

Don't forget you (UK passport holders at least) need a visa for Turkey!

Indeed, and last year they had the Transfargarasan highway in Romania as a parcours I think, which I would try to incorporate into a route if I was going that way (and not extremely heavily laden maybe).