This is part 9 of the puzzle series Around the World in Many Days. Each part is solvable on its own.
This is a Skyscrapers puzzle. Each letter represents a unique number between 1 and 6. Numbers inside the grid can be thought of as heights of towers located in each cell; numbers outside the grid tell how many towers are visible from that direction in the row or column. A tower is visible if it does not have any higher tower in front of it in that direction. Each number is used exactly once on each row and column. The solved grid serves as a 36-letter Vigenère key to decipher where to find the final answer.
GEGKJ QYHE XSJYCH CAIH HUKJP NQHYTYOPG YL YVB YQFTYGBF HXJ YDPISH GFYWQE VWCJ ZLFHEK QSCR HEDLJO SCYSE SIAQAKUQJ
Today I have visited a remote city once filled with unimaginable riches. Can you guess where I am?
Gladys will return in Behind Great Walls.