Venturing in to Old City during layover

You could do it if you're really flexible (it may be quite rushed) and such a short time is worth it to you. You likely won't be able to have a leisurely sit-down meal unless you are willing to trade off seeing a lot less (or hardly anything). Maybe the compromise would be to grab something quick like a kebab, etc. - you'll have plenty of easy choices everywhere.

What time are you getting in and have to leave? On-time or early landing, traffic to/from the airport, and the passport control/security lines will be the key factors because you'll need everything going in your favor - 7 hours seems like a lot of time, but it may end up being tight because you also have to factor in transport time to get to/from the Old City (anywhere between 30 minutes and over an hour in case of really bad traffic by taxi, or 45 min to 1 hour per public transit). I guess you have to ask yourself if is it worthwhile to have 1-3 hours max (I think 3 hours might be overly optimistic) to walk around and pay 20 Euros for an exit Visa to leave the airport. If security has been tightened recently (which I suspect it will be), then it will be even more challenging to have a quick detour to see the city without feeling like you are really tight on time. IST is not a quick airport, especially passport control (big lines). And Istanbul is a bit overwhelming if you've never been before...it would be like going to NYC for the first time on a long layover (sensory overload made worse by lack of sleep on the flight). Maybe you can just play it by ear and see how it goes? If your flight gets in late and that 7 hour layover window shrinks, then you'll probably be out of luck altogether.

Some good feedback. My enthusiasm probably is setting me up for an unrealistic adventure -). Flight arrives IST at 1010 on Delta. Connecting fight departs at 1835.

If you pre apply Turkish visa online, it is around $20US. Airport security prior to 11/13 was already very tight, so I imagine it is more so now. They even check BEFORE entering the airport building itself, plus further checks once inside the terminals.

You may have to consider whether it is worth all the hassle and cost for a possibly short stay in the city . You don't mention when you will be there. Weather may be a factor to consider.

One more thing, Agnes compares Istanbul to NYC. Yes, but it is a bit different:

1. Streets are not straight, and they are hard to walk on because they are all cobblestones.
2. Signage is mostly Turkish. Some English is for touristy stores/restaurants.
3. Depending on time of day, there are lots of touts enticing you into their establishments, creating a sense of blockage.
4. Sidewalks barely exist , often blocked by other stuff or other people.
5. Terrain is not flat, can be steep in some places.

I didn't mean to discourage you because it is doable provided you are flexible, organized and can hit the ground running by noonish and leave for the airport by 3:30pm (it also helps a lot if you're an experienced traveler and have no luggage of any kind weighing you down). It is true that once you get into the neighborhoods, there are a lot of Ottoman (non-straight) streets - the Grand Bazaar is really tricky that way and full of passages leading in every direction. So you'd have to concentrate on what's easy and doable, and have your route planned beforehand. I doubt you would get lost if you just follow the tram line from Sultanahmet (Old City) down to the Galata Bridge (maybe a 15-20 minute walk)....or if you follow one of Rick Steves' walking tours that are not too complicated or just walk in/around Gulhane Park which is adjacent to the Archeological Museum and near Topkapi Palace. The Old City is pretty tourist friendly - you have easy markers like Haghia Sophia and Blue Mosque etc that you can use to orient yourself and there are swaths of space that are off-limits to cars.

Check out a map of the area and see if you'd be comfortable with it (or identify any specific walks in books, etc.), but definitely don't do it if you're really tired from the flight or if you feel like it's too much. if you don't end up going, try to get there some other time when you have more time to spare - the city deserves at least 3-4 full days. Good luck!

If you spend 2-3 hours in the Old City, you'll be in grave danger of wanting to see more. Beware - you'll already be planning a trip to Turkey while you're standing in the security line back at the airport.

I would probably try it. You will have 5.5 hours net. Check the travel time to and from the airport at the time of day. Istanbul traffic can be miserable. My guess is you will have 3.5 hours to sight see. You might hire a guide with transportation to pick you up at the airport.