I am booking tickets for a summer trip. One has a layover in Istanbul for over 8 hours. It would be evening after Blue Mosque, etc. are closed but are they open to walk around the grounds and outside? I am assuming that there is a vibrant nightlife that would be fun to walk through in the hours around midnight. I would need to get a visa to exit the airport. Do I buy this at the airport or before hand? How much is it? Is it worth it for 4 hours just to see the outside of the sights and see some nightlife?
We had the same idea in September this year on an Istanbul layover in between Romania and Hungary. After excluding about an hour into the city from the airport and an hour back to the airport, the plan was to have about 5 hours on the ground in the city. I emailed Umit Yildrim at Examplar Travel Services in Istanbul beforehand, and he met us at Arrivals. We travelled into the City in his Mercedes van. I purchased the visas online in advance ($60 USD each) to avoid the time involved in getting that at the airport.
In the end, our Turkish Airlines flight leaving Cluj Napoca (Romania) was well over an hour late, so we ended up with under 4 hours on the ground. As a licensed guide, Umit expedited us into the Hagia Sophia and the Underground Cistern, we had lunch at an outdoor cafe and did some walking around. It was not a cheap 4 hours ($60 USD X 2 + €160 + entrance fees + lunch X 3), but I have no regrets.
It was our first (brief) time in the City, a primer for a longer trip someday.
Is it “worth it” to you? Your call on that one.
Another thing. If you're flying Turkish Airlines, you might be eligible for their "Touristanbul" program. These are organized tours of Istanbul for their passengers on long layovers. We couldn't take advantage of it as our arrival time at IST didn't line up with any of the tour departure times. More information is available on their website.
The few times I was out after around 11 pm, it seemed to me the city was pretty quiet in the Sultanahmet quarter, where the Blue Mosque and the Hagia Sophia are. I wouldn't recommend wandering around alone, not so much out of concerns for safety but just because if you get lost, there may not be anyone who speaks English who can help you. Maybe the area around Istaklal Street on the other side of the Golden Horn is more lively. It is also farther from the airport - assuming you will still be using Attaturk. They are opening a new airport and gradually moving over from Attaturk, the new airport is farther from the city and AFAIK the ground transportation is by bus or taxi.
Allow enough time on returning to the airport for the security checks. There used to be one just to enter the airport, but I don't remember if that is still being done. Then there's the usual security check right after passport control. There is an additional security check at the gate for flights to the US and to Israel.
Book a Business Class ticket on Turkish Airlines. I could spend 8 hours in the Business Class lounge in Instanbul with no problem. It's amazing.
The Old City (called Sultanahmet) where the majority of the tourist spots are is not teeming with nightlife, nor is it "happening" late at night. If you want a semblance of liveliness, you'll have to go to Istaklal Cadessi near the Taksim district or to one of the nightclubs along the Bosphorus. Going through passport control in one of the business airports in the region will also be painful. I would honestly consider how you're going to feel when you land....I'm guessing tired, groggy, and perhaps sleepless (I'm guessing you'll be on a red-eye flight?). So it depends if you want sensory overload for another 8 hours which will screw you up even more the next day. Don't get me wrong, Istanbul is great but it deserves so much more time than 8 hours in the middle of the night. If you're adventurous though and don't care about being in a very dense environment which is like a giant bazaar, then go for it. I just wouldn't park myself in the Old City though, because it will feel too quiet and you'll stand out (the touts in Istanbul are nice, but persistent). The Visa can be purchased online and it's only about $20 or so.
I dont think it will be a feasible option. When you fly here, its going to be a new airport and it will take about 1.5 hours bus ride to Central Istanbul. If Turkish Airlines have that free tour, then you are fine.