One of the places you need to visit when you go to Turkey, like in specific, is you need to go to Cappadocia. Cappadocia has a bunch of Christian history, Christian Muslim history, and a bunch of like cool mountains and like ancient like churches that were built into the mountain and it has this thing called like the underground city, so make sure you go and check that out if you get a chance to go there.
Turkey, and in particular Istanbul, is absolutely full of history so there's tons of places to go. But my two favorite places besides the Hagia Sophia, which of course is absolutely famous and everyone knows it, were the Soleimani Mosque and the Dolmabahce Palace. So the Topkapi Palace is on one side of the Bosphorus and on the other side is the Dolmabahce Palace and the Topkapi is really famous, particularly for the Topkapi dagger that has been featured in quite a few really big films, but at least to me, I thought Dolmabahce Palace was a lot prettier. And the Soleimani Mosque, unlike the Blue Mosque and the Hagia Sophia, it is a bit off the beaten path and several blocks away from the main square, but it is definitely worth the hike as it is absolutely gorgeous and a really awesome place to visit.