There are plenty of layover day and night tours available to book depending on the time and duration of your layover. It is also incredibly easy to visit the city on your own if you wish to do so. The best place to go will be Sultanahmet Square, or Hippodrome, which you can get there by metro straight from the airport. From Sultanahmet Square, you will be minutes away from the iconic Blue Mosque, Hagia Sophia, Basilica Cistern Museum, and the famous Monuments Trio, which includes the Egyptian Obelisk, the Colossus, and the Serpentine Column. If you have more time, visit the historical Bazaars where you can check out spice products, handicraft goods, and even carpets!

All popular attractions at Sultanahmet Square, along with other major spots, including Topkapi Palace, are always busy during the daytime, especially during the peak season months from April to June and from September to October. To best avoid larger crowds, it is always a good idea to start the day early and visit 1 to 2 biggest attractions first thing in the morning and do that again the next day so you will have the rest of the day visiting smaller and less crowded venues.

Istanbul is a wonderful city to get around on foot. You will be able to find interesting daily sights that will often be missed and observe the local way of life. For further journeys, the bus system in Istanbul will be extensive enough for you to get to the nooks and crannies of the city without breaking the bank. You will need a bus map, available at all bus terminals, and an Istanbul Card that allows you to access all types of public transport, which includes buses, trams, metros, and ferries.

There are free walking tours in Istanbul, especially in the old town area, which vary in length and the number of participants. You are, however, strongly encouraged to tip the tour guide depending on the level of enjoyment and satisfaction you get after the tour. Therefore these tours aren't technically "free", but you will certainly be paying a lot less compared to other private tours with similar itineraries.

Generally, it is safe and fun for solo travelers to visit Istanbul. Just like anywhere else, there are still precautions to be taken, such as the clothes that you should wear or proper maps and directions of the places that you want to see. In Turkey, female travelers should pack conservative clothing to wear during the stay to attract little attention. Get a data SIM card so that you can navigate around more easily and book tours, in advance or otherwise, if you're not feeling 100% sure to explore on your own.