Please check the maps
On the second picture is information about a key, do you maybe mean that one?
Edit: Here is further information on the keys. They look very similar.
There it says that you find a dark blue key in the hanging gardens, you will need that one for colossus of Rhodos. For the hanging gardens itself, you need the light blue key, that you find in Tempel of Artemis at Ephesos.
So it’s not „that same key“. You have the dark blue one and need the light blue one.