There are many defence structures around Azerbaijan for this tentative site and half are in Baku. Like most people I only visited the ones in Baku and I even did it in two parts. The ones at the sea further northwest are on a road you would be taking a tour bus on and private car wouldn't be worth going that way anyway. Previously I had visited Mardakan in the northeast PAST the airport. This time I did the other three. First, and easiest, is Sabayil Castle:

Wait? Where? Well, the castle is gone and only the walls remain UNDER the water. You can see it from the bay which you probably visit for the "epic" views. Baku Eye wasn't running and it was super hot but it was still a worthy visit. That there is an old castle in the bay wouldn't be known to just anyone. The most obvious pointer is a sign, a second would be the map we have. There is not much to see but birds (and those are boring sea gulls or ducks).

Second visit was Ramana Castle which most people use as their picture. The main reason is that it looks pretty good. You can see it from miles away and it's quite glorious even from close by. You cannot enter it even if they seemed to have plans to have visitors.

Third visit was Nardaran Fortress which is north of the town and maybe out of the way for most visitors. It was also not open and looks similar to Ramana from the outside. It's higher and has great corner towers. So all this isn't all special because most castles in the world will have similar styles and they are open, have more to show, and are after all just remnants from the past. The whole idea is that they were used as defence at the Caspian Sea. I'm not for inclusion and I don't even recommend seeking them out but as some are IN Baku you may as well stop by for a quick visit. Sabayil might easiest but definitely not best of the bunch.