I took all the trophies and enigmas. After the last enigma I got an incoming transmission (if I understood, it was to tell me where Edward Nigma is located) but I didn’t understand perfectly.
On the map there is nothing. So where is the Riddler?
My understanding was that he wasn’t actually on the island, and when Batman collects all the riddles he deciphers the location and sends the police there. I recall hearing Edward Nigma being arrested over the radio transmission.
A slightly disappointing conclusion to the long search for riddles, perhaps 🙂