This is the bonus cache for the Lab adventure "Henley Coastal Mosaics".
Each answer for the 5 lab stages gave you a colour and a number. The 5 numbers will give you the southern minutes and the 5 colours with the right conversion will give you the eastern minutes.
It's up to you to work out the sequence. What I can say is that the sequence is the same for the lattitude and for the longitude and that you have already walked past GZ, so it shouldn't take many guesses.
There is a convenient nearby bench where you can log your find and enjoy the views.