Aira

A golden city, remembered vividly enough by one lifelong searcher to sustain an entire unnaturally long life spent looking for it — and revealed, by the one witness positioned to know for certain, to have existed only as a lonely child's story about himself.

Whereabouts: Described only as a marble city of fountains beside a warm sea, by a single source whose own account is eventually contradicted by someone who knew him before the description started.

Access: Never independently reached or verified; the one witness who might confirm its existence walked into unstable desert sand rather than provide a final answer.