London

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Across
  1. 2. Oldest continuously occupied castle in the world
  2. 4. Historic English castle once used as a prison
  3. 6. Major Welsh fortress built by Edward I
  4. 7. Strong central tower of a medieval castle
Down
  1. 1. Known as the “Key to England”
  2. 3. Early Norman castle type with mound and courtyard
  3. 5. Scottish castle built on an extinct volcano