I agree with DW, The red emerald was good hiding spot, also the orange emerald too, I couldn't find it anywhere for 3 minutes the first time I played it X_X.
Yeah, just look at the gargoyles, find secret floors/areas both in water and land areas, (Also look at the back of objects e.g. FOF's. By a waterfall, go to the back, and jump, or stand on the top of the waterfall, and carefully fall down whilst staying there, you will have a surprise.