Looking for some opinions. For my own flight patterns I'd be interested in Europe, but there may be some others who are willing/able to talk about other airports in other places.
I recently had a couple successful flights taking layovers of 8+ hours through LHR and going into London and seeing some sights - when we do flights again, I'm looking to either fly through London again and see some other sites, or to pick a new country/city and explore.
Knowing a suggested amount of time needed to see some sights would be useful. I know I'd not suggest a shorter than 8 hours for London (possible, but 8 felt just right to us), and probably no shorter than 6-8 for Istanbul.