To elaborate on my earlier idea about skyscrapers and an urban environment today walking in Chicago I stumbled across the obvious choice I never thought of before. There is a skyscraper in Chicago with a mountain relief on it! It is One Prudential Plaza and it was completed in 1955 so it would fit in with the times of a 1960ish movie setting.
Here are some pics of it:
The first picture shows the building in relation to skyscrapers of today, those other skyscrapers would not be there in an Indy time frame, the other two pictures show you exactly what I am talking about with the mountain.
It would be awesome to film part of the movie in Chicago in addition to having part of it set there. The Indiana Jones saga has two connections to Chicago, within the fictional context Indy went to the University of Chicago (where they could film the college scenes, even if they still pretend its Marshall College as in the others). The real world connection is that Chicago is Harrison Ford's hometown. Chicago has seen alot of great movies filmed here, Harrison Ford filmed the Fugitive here, more recently Batman Begins, the Dark Knight and currently Transformers 3 is being shot here and this would be another great blockbuster to shoot here in part.
Obviously the movie should include lots of globetrotting, more so than KOTCS which was filmed entirely within the US and its setting was strictly the Western Hemisphere.
Here is how envision the opening scene. There would be the paramount logo that fades into the mountain on One Prudential Plaza then the camera drops to show a silouette of a man in a light colored formal suit holding a briefcase and wearing a fedora looking up at the logo (think Indy at the train station in KOTCS but from behind) with hordes of pedestrians walking by like its rush hour in the big city. Somewhere around here the caption will say "Chicago 1962" or thereabouts. The man enters the lobby of the building, removes his hat but we still only see a familiar looking grey haired head from behind. He descends down to the train station level (there is a commuter train station down there) walks around the train platform and a conductor says "South Shore Line to INDIANA, all aboard!", the man boards the train quickly, runs into a lavatory, as the door is closed the train starts moving but not ten seconds later the door opens and Indiana Jones emerges dressed in his usual leather jacket with a whip and the fedora. He hurries and jumps off the moving train to the puzzling look of the conductor. He waits for the train to go by and then opens a manhole cover (the train platforms there are already underground) and descends further down through sewers and freight tunnels (common in old Chicago) and eventually what looks like caves or primitive tunneling. He stumbles across the remains of Fort Dearborn, (the first permanent white settlement in what would become Chicago) but Indy is looking for something older, some native american artifact relating to the pre-history of the city.
That's all I can think of for now, its an idea that maybe needs to be fleshed out a bit more but its a start. Of course this is the pre-adventure and probably not related to the main McGuffin.