Next to Hell is the turtle farm.
But, I must say that aside from getting "the thrill" of sending a postcard from Hell, in my view, it's a bit of a waste of time.
Grand Cayman also has expensive shopping, so not great for that.
I do enjoy just going to Seven Mile Beach.
The very best thing to do in GC, if you haven't been before, is a trip to Sting Ray City. Fun and pretty original.