Human-made wonders

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Across
  1. 3. sports area with many seats
  2. 5. underground passageway for cars
  3. 6. public open space
  4. 8. tall structure with a light on top
Down
  1. 1. artificial structure for boat navigation
  2. 2. elevated road over a river
  3. 4. underground railroad
  4. 7. a very tall building