A lot of thought and prep time has clearly gone into this puzzle and all it subsequent updates. I will attempt to do its complexity justice by answering your 12 summary questions in order, providing a few diagrams along the way...
Tell me the "most obvious" thing I could type into the box to actually locate a few towns.
Tell me where some (or all!...
Posting this as a partial because I don't have time to devote half enough time to the wonderful array of clues provided, but I think the secret is
Take for example:
EDGBASTON: Comes up to a place near the M5, south of Eastington. If you actually want Edgbaston, keyword STODGY will get you there, specifically to the golf course.
keyword STODGY ...
To continue on from @Phylyp's work - they were first to realise the encoding mechanism for the message:
Using a very manual approach to the decoding, assisted by some Excel formulae which allowed me to keep tabs on the current possibilities for each letter, I have now fully decoded the initial message (punctuation mine):
What next? Note ...
Partial answer: from images to codes
In Brazil (first time), the coloured regions are
In France, the coloured regions are
In Australia, the coloured regions are
In Turkey, the coloured regions are
In Sweden, the coloured regions are
In Brazil (second time), there are no coloured regions.
In Germany, the coloured regions are
In the Netherlands, the ...
I want this to be a comment on the 'spanish thing' but for some reason I can not enter a comment.
Gurer ner n ahzore bs fcnavfu jbeqf uvqqra va gur jbeqfrnepu tevq. Gur barf V sbhaq ner Yhan (zbba), Fby (Fha), Fhq (Fbhgu), gvha (lbh), fna (fnvag), cn (sngure), rf (vg vf)
The country your sister most recently visited is:
The last step:
Some final notes:
Regarding the handwritten note:
A final easter egg:
I absolutely loved this puzzle! It hit the exact blend of "curse you" and "a-ha!" moments to make for a really enjoyable time. I sincerely admire the ...
I can't solve the entire message, but here's a start. I'm happy for someone else to take this idea forward in their own answer.
The encoding works - at least in part - like this:
Unfortunately for me, I've not been able to make any more progress after that, and it doesn't help being on a mobile either!
I have a suspicion that this bit of the puzzle:
I think the answer depends on what "going east/west" means. That is:
Under this definition, suppose you start from P1, walk south to P2, east to P3, north to P4 and west to P5. (Each walk is 10 miles long.)
I check the following three cases.
Part 1: The Solved Grid
The solved grid is below:
The logic for the left side portions was relatively straightforward. There were no particularly difficult steps - just searching for the next place progress can be made, like solving a jigsaw puzzle.
A few sections had extra information that seems important:
Part 2: The Messages
Partial: Criss Cross and Three to one solved
(There are three letters missing to the right of ‘Three to one’ that I can’t yet place without solving the bottom right area)
Three to one:
However I know that Deus has all four parts and is looking at the next steps so I expect this to become obsolete :) Still very fun to solve!!!
Edit: congrats ...
Ok, here is my attempt to so far.
An old comic strip of some people in an office.
Betting stubs from New York, seems she hit a trifecta!
Medical photos of her feet!? Gross.
A well-worn music festival bracelet with the Spanish flag on it.
Her tour itinerary for a trip London, seems she went to the Olympics and parliament.