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
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 ...
Extending @QuantumTwinkie's answer, and using the connect-wall tag, notice that there is a connection between each group of four words. (Note: I never would have gotten this without QuantumTwinkie's answer, so this is a true tag team effort.)
DUO, IRON, LINKS, ROCK
ICE, LED, METAL, TIC
DRILL, PI, WIN, WOO
BRA, IGNITE, LOOM, RUBBISH
AIR, DUST, GO, PAT
Now Complete Answer
The first thing to notice is:
To represent the solution:
The first steps:
At this point:
Using the funky square:
Some more funky square logic:
Some perspective after sleep:
One final logical step:
You are going to:
And the Safe combo is:
I had no idea where to start with this, so did some cryptanalysis. The Index of Coincidence was $0.04082$ suggesting a polyalphabetic cipher (therefore likely vigenere), and running probable key lengths suggested that the most likely key length would be 8. Now things started to fall into place!
The first important ...
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 ...
You, the self-critical author, think this puzzle is
P3 of emanate
C6 of maniac
F5 of paroled
O4 of throne
G11 of seashore
P7 of raptor
The answer is
Ringtone followed by an umberlily
A burly lime precedes a foul rein
A grin note
A con bar with eg. Onyx
Put together we have
A Gerbil OBE is French
Before starting off, I just want to state that I don't know the proper formatting, so the answer might be downvoted. Also, I might be pulling at straws for the most part, because I am just an engineering student trying to apply his brain at some puzzles, but here goes nothing-
My first guess is that all (or at least some) alphabets have a number associated ...
Since there are surprisingly few two-player games with dice and black and white pieces, I think they were playing
In this game, the highest roll is
This should give the cheater a landslide victory over a random player.
However, even a little strategy goes a long way against such a single-minded cheat: by rolling, say 1 and 6, the cheater's two farthest-...
Okay, let's take this step by step. Because what we have here is a type of treasure hunt (as per the title) more commonly known as:
The diagram at the bottom of the puzzle depicts:
How do we know what to do with this? Note that:
What do we find here? Another treasure hunt puzzle!
So let's solve it...
How to solve ...
Some things that appear not to work
Normally posting answers that merely try things and fail is frowned on around here, but in this case I'm making an exception, since it's been a few days and the question has been bountied -- and also because the things I've tried seem to be very much the sorts of things the question hints at, and it feels like I've tried ...
Here some of an attempt heavily inspired by other posts
I number the lines of the poem
(1)Some see de earth vill end times four,
(2)Some see de t'rice.
(3)From vot I've tasted of de four times,
(4)I and zose who know for whom it vas.
(5)But if I must perish twice ...
(6)I am enough of 'ate
(7)To see zat it is for destruction
(8)Zat de ozzer is really won.
Al Zimmermann's Programming Contests match this description. The name includes "programming" but does not require it:
You can enter whether you use a computer, manual calculations, or tea
leaves to solve the problems. You send me solutions, not programs.
The current contest ends on July 18.
Here's my attempt!
Some see de earth vill end times four,
Some see de t'rice.
From vot I've tasted of de four times,
I and zose who know for whom it vas.
But if I must perish twice ...
I am enough of 'ate
To see zat it is for destruction
Zat de ozzer is really won.
Now, vhich is vorth most?