Anchor: Some 500, mostly ruins, can still be traced, but only 30 are visitable.
Entailed: 500 ruins can still be traced but only 30 ruins are currently visitable.
Contradiction: 500 ruins can be still be traced but not 30 ruins are not vistable.
Contradiction: A group of people walking beneath an arc made of ham.
Contradiction: The people on the island are all very happy.  
Contradiction: There are people watching others play instruments
Contradiction: Barnes and Noble might put mid-list novelists out of existence.