At the end of chapter 59 of "Innocents Abroad" Twain wrote:
The ship had to stay a week or more at Gibraltar to take in coal for the home voyage.
It would be very tiresome staying here, and so four of us ran the quarantine blockade and spent seven delightful days in Seville, Cordova, Cadiz, and wandering through the pleasant rural scenery of Andalusia, the garden of Old Spain. The experiences of that cheery week were too varied and numerous for a short chapter and I have not room for a long one. Therefore I shall leave them all out.
Did he ever write anywhere else about what he experienced in Spain? Not that I recall, but maybe I am forgetting or unaware of some obscure text...
- B. Clay Shannon