yes great hill is the one you mean but it is straight in front of you from the top of Winter hill – ie to your left when you start the san marino descent
you cannot really [ you can but dont] get there from the Blue lagoon without either aswamp or a push.
I would avoid as it is best done after lots of sun or in winter when the grund is frozen as it is very boggy.
If you e-mail me [ yours is not in profile mine is] I will send you some MM routes to et to Healey nab and show you the best routes up great hill from belmont road side