You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: SCIENCE FICTION 
Clue: A recent re-issue of this Sir Arthur Conan Doyle novel includes an introduction by Michael Crichton
the lost world

Category: GEOGRAPHIC PHRASES 
Clue: Mythological name sometimes given to Mount Acha & Gibraltar
the pillars of hercules

Category: LANDMARKS 
Clue: Some of its pieces, which weighed up to 50 tons, were quarried at Marlborough Downs, about 20 miles away

stonehenge