World mysteries crossword

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Across
  1. 2. Egyptian structures aligned with the stars (7 letters)
  2. 3. Remote ocean point, farthest from land (4 letters)
  3. 4. Advanced civilization said to have built the pyramids (9 letters)
  4. 6. Legendary underwater city said to have sunk in a day (8 letters)
  5. 7. Ships and planes go missing here — spooky triangle (7 letters)
  6. 8. Unidentified flying object (3 letters)
Down
  1. 1. Theory that time isn't linear (7 letters)
  2. 3. Mysterious Scottish lake monster (4 letters)
  3. 5. Extinction event linked to an asteroid (10 letters)
  4. 6. Alien hotspot in Nevada (2 words, 4 + 2 letters)