Solution to The Curse of the Atlantean's Tomb

These are cryptic clues, except that in some cases the wordplay and definition halves indicate words that are one letter different from each other.

If you read both halves of those one-letter differences in order of the grid, you get the cluephrase: IN CO AS TA LC AL IF OR NI AR IG SU BT RA DE LI MI TS

(The order of the letters in the bigrams is ambiguous -- use your judgement to make a phrase).

Solve this final clue to get BIGSUR.