Europe isn't Africa (thanks god!) - I understand that 60£ for a RT on a mid-haul (if you call 4hrs that) is considered a steal, but then it's not something completely uncommon. IST right now is pretty much "meh" of tourists, and airlines are dumping prices there left and right (I've just flown it for about 55£ from ZRH with LX, RT) - so while TK 61£ certainly is VERY attractive, it's NOT an error fare or anything like that, it's just a low-fare used to get people to fly to IST.

Edit: Just check it yourself:

https://www.kayak.de/flights/ZRH-IST...-16/2016-11-23

85€ Ex-ZRH, for example - much cheaper on "Atlas Global", same route
Most German airports are about the same.. STR 90€, TXL 91€, FDH 82€
Ex-CDG, A3 can be had for 89€ RT to IST.. ARN with TK is 98€...
Ex-MXP, A3 again is cheapest, 73€ (which is less than TK's 61£ Ex-LHR) - this can earn you much more than TK's miles, if you use it right..

All very similar to the fare Ex-London..

All I want to say is, good offer, but nothing really you should get crazy for. It's regular entry-fare to IST, not just on TK, but to be found similar on many airlines with destination IST Ex-Europe. I wouldn't call it "a steal" if you can book it with many different airlines for similar or even cheaper fares.

If you're starting in London, then yes, it's a good fare if you want to fly *A to IST - but apart from that, the fare isn't really "special"..