A few of my favorites:
The piano in "Me Ship, the Olive". Play the colored keys (in the right order) for a surprise.
When heading into Suess Landing, veer to the right, down to the water, to "Sneetch Beach", a place most people don't know exists.
Just past the bridge to the Lost Continent (as you leave Suess Landing), there is a smaller bridge heading to Mythos. Stand there quietly and see if you can hear the troll.
And there's plenty more than those ...