Thanks, if I have any specific things to ask, I know where to turn 
No, as I’m only there for four nights, I think I’m going to make the most of the time just in the city rather than trying to fit in more. (Possibly doing the trip on the Bosphorus being an exception.)
The Blue Mosque; TopKapi Palace; the Roman cisterns; the Hagia Sophia mosque/church; someone mentioned Dolmabahce Palace, but frankly, I wasn’t impressed. It is an Ottoman copy of a typical European palace. Why go to Istanbul to see that? If you can arrange it, take a sunset cruise on the Bosphorus to see the city from the water. The Grand Bazaar and Spice Bazaar are both well worth visiting. I had a pofessional guide, who some folks say is the best in Istanbul, so I had a very nice time. Defintely do a bath if you get the chance. The nice hotels will have them, called Hammam, and there are many free-standing and much cheaper baths around the city. I love a good scrub, though you might find that the marble table you are stretched out on is a little warmer than you might find comfortable. Enjoy yourself.
Bumping the thread on my return 
Fantastic trip, from start to finish. Everything worked out perfectly - changing hotels was the right decision, I was in just the right place, near the Tünel and so within easy reach of everything either by walking across Galata Bridge or by tram and ferry, and I was surrounded by restaurants frequented by locals. I felt like I was eating more than I normally do, but on removing my belt for security checks on the flights home, discovered I had lost a bit of weight. Two flights feels like a real hassle when that’s the case! I was also perfectly positioned for getting to/from the airport - the Havas bus to Taksim Square did a stop close to my hotel, and I did the return journey by tram & metro almost without breaking sweat. Well, I’d nearly acclimatised.
As I expected, the Blue Mosque and Aya Sofia were deluged with tour parties and were slightly chaotic. But as I’ve found with similar situations in places such as Notre Dame and York Minster, if you concentrate on the building alone for long enough, you can block out much of the distraction around you and take it in properly. At the Blue Mosque I was helped out by one of the men checking everybody’s clothing was appropriate, who clearly wanted a break and decided he wanted to ‘tell me a story’. I knew what was going on, that he was going to be my ‘guide’ and was after a bit of cash, but I was happy to go along with it for two reasons. One was that I got to sit down along the side of the building and take it in more fully than being stuck in the tourist area along the rear. The other was because I felt mischevious, and instead of chatting with him or trying to conclude things, I’d just let him talk…and talk…and bullshit…and desperately bullshit (like he really knew how many tiles were used to line the building?!)…and eventually, after a very pregnant pause, the inevitable ‘So where you from?’ At that point, I put him out of his misery 
Possibly due to doing a lot of walking, which is what I always like to do when going to a city for the first time. I was certainly grateful for the endless supplies of cold water on sale just about everywhere, including kids with buckets of ice filled with bottles (respect to the lad who’d spotted the opportunity, and had the resilience, to stand outside the tourists’ exit from the Blue Mosque, where they were coming from the cool calm inside to the fierce sun right in their faces).
The Grand Bazaar left me underwhelmed, perhaps because the guidebooks build up the expectation too much, or just because I don’t give a toss about carpets or gold jewellery. The Spice Bazaar, however, was just right (good call, Shamozzle). Even though it has a touristy element, it’s not only touristy, especially when you also explore the adjacent streets, and it was damn good fun. Knowing what’s going on, and having the intention of actually buying stuff, it was entertaining to let the sellers suck you in to their whole show-you-everything-they-have routine, because they’re just so damn good at it. I’m pleased to say that in the cold light of unpacking, nothing I bought seems like it was an impulse purchase. So either I was smart, or they’re really good.
Highlights, some anticipated, some unexpected:
The ferry across to Kadıkoy, purely for the view of the city. I sat for ages on the harbour wall their, just looking & watching, both the city and the shipping. Also, taking up a seat on the outside benches along the side of the ferry, I noticed numerous locals (I presume) were still clearly taking in the view with pleasure for the duration of the journey.
People-watching at Eminönü. I love doing it at London railway stations in rush-hour, so doing the same in such an environment, on a harbour with the overwhelming smell of frying mackerel, was fabulous. And, at the same time, boat-watching: the way large ferries could be operated with such seamanship to make them work as a mass transit system was fascinating. (I think this was the hot weather alternative to Kyla’s suggestion )
The view of the Black Sea at the end of the Bosphorus cruise. The trip itself (on the public ferry, not the private excursion) was interesting rather than gripping, but also good relaxation after two days of slogging around in the heat. My guide book lied about a ‘30 minute walk’ to the castle at Anadolu Kavagi. It is actually a relentless climb, half of it up steps, with no redeeming features at all. I was so glad I’d brought a big bag of the delicious strawberries where were on sale everywhere, which I devoured with messy glee while watching tankers and container ships disappear into the haze, which never quite lifted that day, and so kept the rich blue sea blurred into the beginnings of sky.
People really being as friendly and helpful as I was led to expect, which is a first. Stopping to check on a map that I was going the right way, a podgy middle-aged man literally ran across the street to help out, and wouldn’t stop until he’d made sure that I knew which way to go if I wanted to go to the Aya Sofia, or the Spice Bazaar, or the Grand Bazaar. Shop staff, all other sellers, and waiters all immediately talk to you in the Universal Language of Tourism (not money, but English!), but also tolerate and humour attempts to use Turkish. A welcome change from the snootiness of Italians and the petulant French, for sure. It’s a city which lives to trade & sell, and above all else, they clearly know that keeping the customer happy is paramount.
There’s obvious omissions from the itinerary. I knew I couldn’t do everything, and so had decided before I arrived that the Topkapi Palace and Archaeological Museum were for another time. In the same way that I wouldn’t advice a first-time visitor to London to try and do the British Museum and Tower of London in one day, I suppose. I’d hoped to visit a Hamam, but simply didn’t get around to that one. No regrets, though, because it’s one place that I know I want to return to (and I don’t say that about everywhere!)
I’ve put up a handful of photos here - I’ll do more if you want
Still, a Turkish delight, on a moonlit night!
I’d suggest touring the old palace of the Byzantine emperors, but apparently it no longer exists.