We stayed in the Side Hotel about 9 years ago, absolutely fine, very clean and safe and absolutely central ie between the Blue Mosque and Aya Sofia. Sultanahmet is the place to explore - the modern city is beyond dull, unless you like Thurrockalike shopping malls. We walked most places from there, eg to the Topkapi Palace. The national Museum is great, and very under-visited, also close to the Topkapi. The Galata Bridge and wharfs are brilliant for just watching the manic crowds, but the restaurants there are fearful rip-offs. The streets on the downhill, eastern side of Sultanahmet, dipping to the river, were a bit unfriendly when we were there - I think there may have been issues surrounding compulsory purchases that made the residents very glum and angry. Visit the Cistern! It's much better than it sounds! And of course the bazaar by tram - that was the only transport we took, apart from the open top tourist bus, which was hopeless and simply pulled over and stopped. Prepare to have the living daylights mithered out of you every time you stop walking briskly. Everyone and his brother has a carpet shop, and they open up by politely asking if you like their city, where are you from, yadder yadder. The biggest scammers are guys in cute turkish national costume in the green space near the Blue Mosque. They carry huge tea urns on their backs and pose for photos, hand a cup of tea, then start demanding vast sums of cash. Also, little boys have a habit of throwing stones, but I think that's a thing all over Turkey.