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Your best friend Alex is great, but she's a bit too into puzzles for your taste.

Today, she sent you a package. It included a letter informing you that she’s planned the adventure of a lifetime for the two of you for next year… if you can figure out where the adventure will be, and the combination of the safe in which she locked the plane tickets (well, she probably just printed out the email confirmation, but you get the idea). It’s locked with a four letter code. Yeah, she mailed a small safe for the sake of a puzzle. That's Alex for you.

All you have to go on is this note she included with the letter:

My dear friend and fellow adventurer! 
I’m so excited to travel with you. 
The lines may be long at the airport, 
but they’ll be worth it once we get to our destination. 
Unfortunately (please don’t be cross!), I locked up the tickets 
and you’ll have to solve a puzzle before we go. 
It shouldn’t be too difficult; 
just start at the beginning.

On the back of the note is the following block of text. Looks like gibberish to you, but you're pretty sure it's not. It is Alex, after all, and this is a lot of nonsense to painstakingly write out in all capitals like this.

OWGUCNCNNFQYRXFGPTUGJBN
MWJEIVFCAJWHPIOFTSWKQZD
DTSTBWEKOGAFQYRXYUMSCGV
RNURZXCILFXJJKCFQXBUTKO
JRTPHTSHRXWGJFQYVPOUQLH
DLOWOPRUYIOWXAWQFQLZRNG
KHFWXUMQQYRXFXJFQYRBXNX
NKPVVXOUKIYIOWXAWHYQPZU
QXKLBOAMXAQYROFGJFQXYLL
MQMESJETBDJFYIXNYWAWLIG
RNXOBEFPNXSQQPRBTPWXXSF
GSYWRXPXHJUSFQYYKLSEPED
NHMLALXTNAZCEWGOYXBUUVX
SJFTPWJCMXPNRNSYMAKOSXT
DDVMNNUZCTXPWCXPDCGFRMZ
LHDFHXOALESJDTOWOCCDDFN
PWZMJEWRKJEHEFRYIWWMZKI
LYFEAXOOTUJEHJRWBWMBSFF
JUSWKLZJKUPXPPXKTKVOHED
RXCAOECEDRYUODSYDQTETLP

And finally, right below that, scrawled in a different color:

FCJLIRJVYHNXQASSRKHVNCEDYPMSEBZEWWDBZFLVBZIXIOOIGWHVTCQEYGHPFYTNTZXXVHTUFGXFQYORROXXCARWTSIIFQXMHWGZGWENGEZHSVWPFCYELEZXLGZIAMTLAHIYGDLAGZCMSXDFMWRDVYKIIFWWTZPL

PLEASE NOTE: the original had a copy-paste error with one letter missing, and the updated scrawl is here:

FCJLIRJVYHNXQASSRKHVNCEDYPMSEBZEWWDBZFLVBZIXIOOIGWHVTCQEYGHPFYTNTZXXVHTUFGXFQYORROXXCARWTSIIFQXMHWGZGWENGEZHSVWPFCYELEZFXLGZIAMTLAHIYGDLAGZCMSXDFMWRDVYKIIFWWTZPL

So, where the heck is Alex taking you, and how will you open the safe to get the tickets?

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    $\begingroup$ Pretty certain it’s some sort of polyalphabetic cipher (likely vigenere?) based on the IC value, and the IC for key length suggests key length is most likely a multiple of 4 (and most likely 8). No idea for the key however, but perhaps there’s a hint somewhere in the first piece of text... (just throwing this out there as this is as far as I’ve got) $\endgroup$
    – Beastly Gerbil
    Jul 13, 2020 at 18:22
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    $\begingroup$ @BeastlyGerbil You're on the right track! $\endgroup$
    – kristinalustig ♦
    Jul 13, 2020 at 19:50

2 Answers 2

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You are going to:

Spitsbergen!

And the Safe combo is:

SSNR

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 piece of information is the line:

'just start at the beginning'

So...

Taking the first letters of the first sentences gives us the 8 letter key 'MITBUAIJ' and using this as a key on the ciphertext gives: 

CONTINUEBXXXXXXXDLBFPBF
DKBLHBFURXOOOOOXKGORPFD
VKGLIVKKGXOXXXXXQLAKJFB
RFLFREBOLXOXBRBLQPSILRN
PRLGVLZGXXOXXXXXBPGLEDO
CROOFDJBXOOOOOOXEWLRIBY
RGLWPLAIXXXXXOXXXXXBPEL
FROBVPFICPXOOOOOOOXWPRL
EPRKHOSDLSXXXOXXXXXWELD
DEELRPELSRBMXOXFPKSDKOG
JELGIDLPFOGIXOXBLGKPERL
GKPKJEODHBLGXXXEKDJSHLC
THECODESTARTSONNEXTLINE
RPFLGKBJLDPFIBKFLGKGJLL
KCBMFEIRJSDPOTLHKBMFJDN
DOCLHPFODLRPDLFKGJBJDXE
DOGLPEOIYBLGKFJPWODLFKA
CMXLZDOGKIBLGPROSKEIRLF
BLGORKFJCLDPWODKLBJGODJ
RPTOGLBKDJPIGKREDIKSLSO

This says

'Continue' then some other cipher text. Then about halfway through it says 'The code starts on next line' followed by more cipher text.

From here:

There are Xs and Os in the top half of the decoded text. These form a crossword grid: (thanks @Stiv for the image!)

enter image description here

And @Leppyr64 found that using the code in the bottom half as a key on the last string of ciphertext in the question gives:

ONEACHIMNEYSIZINGEXPERTTWOANATIVETONGUELANDOFBLUELAGOONTHREEAONESQUAREFOURTRIANGLESONEDTINYIDEABITSTWODCAPITALSHORTDAYLONGXXXXXXXXXXXXXXXXINTERSECTIONSARECOMBOXX

These are crosswords clues followed by 'INTERSECTIONS ARE COMBO'

The crossword:

enter image description here

(1D is incorrect)

1A: Santa is an expert at fitting down chimneys
2A: The blue lagoon is in Iceland, and 'Iceland' in Icelandic is 'Island'
3A: A pyramid can be formed with a square and four triangles

1D: ?
2D: Norway but I'm not 100% sure why

The crossword clues hint towards the location: (which @MrSethward somehow managed to find a long time before the crossword was completed :P)

Spitsbergen is an island in Norway, with a town called 'Pyramiden' (the pyramid).

And then using the information we have to find the combo

'INTERSECTIONS ARE COMBO' and the 4 intersections in the crossword grid are SSNR.

Very nice puzzle! :)

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    $\begingroup$ Great job with the first part. You probably don't need my confirmation that you got the first bit, since you got something that's not random characters back. :) $\endgroup$
    – kristinalustig ♦
    Jul 14, 2020 at 3:40
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    $\begingroup$ I'd forget the notion of binary for the two symbols you mention - check out the very clear pattern they make in the top half of the stage-2 ciphertext. It looks to me like you could be dealing with something more like rot13(n jbeqfrnepu, n fgerrgznc, na vafgehpgvba xrlvat n genafsbezngvba... fbzrguvat zber culfvpny naljnl, engure guna fbzrguvat rapbqrq cre fr...) $\endgroup$
    – Stiv
    Jul 14, 2020 at 8:28
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    $\begingroup$ Hey @Beastly, nice work on the bottom half. Some ideas: rot13(V guvax BAR FDHNER SBHE GEVNATYRF --> CLENZVQ. Sbe gur ANGVIR GBATHR OYHR YNTBBA, avpr, V jnf guvaxvat vg pbhyq nyfb or VFYNAQ, fvapr gung vf gur bssvpvny anzr bs Vprynaq naq zber trareny. Jvgu gung, V gubhtug A_E___ pbhyq or Abejnl (nygubhtu V pna'g znxr urnqf be gnvyf bs gur pyhr), juvpu jbhyq cbvag gbjneqf Fcvgforetra, na vfynaq va Abejnl jvgu na nonaqbarq zvavat snpvyvgl pnyyrq gur clenzvq be Finyoneq, gur nepuvcryntb vg'f n cneg bs. (guvf ynfg ovg vf n fgergpu un, ohg V'z fghpx bgurejvfr)) $\endgroup$
    – MrSethward
    Jul 14, 2020 at 13:53
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    $\begingroup$ Also, you should adjust rot13(3N hc gb vagrefrpg 2Q ng gur 3eq yrggre). $\endgroup$
    – MrSethward
    Jul 14, 2020 at 13:59
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    $\begingroup$ Also - this is my very first puzzle I've ever made, and seeing y'all work through it is an absolute delight. $\endgroup$
    – kristinalustig ♦
    Jul 14, 2020 at 14:32
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Partial Answer Continuing from Beastly Gerbil's Answer:

Decrypting

FCJLIRJVYHNXQASSRKHVNCEDYPMSEBZEWWDBZFLVBZIXIOOIGWHVTCQEYGHPFYTNTZXXVHTUFGXFQYORROXXCARWTSIIFQXMHWGZGWENGEZHSVWPFCYELEZXLGZIAMTLAHIYGDLAGZCMSXDFMWRDVYKIIFWWTZPL

with this OTP key:

RPFLGKBJLDPFIBKFLGKGJLLKCBMFEIRJSDPOTLHKBMFJDNDOCLHPFODLRPDLFKGJBJDXEDOGLPEOIYBLGKFJPWODLFKACMXLZDOGKIBLGPROSKEIRLFBLGORKFJCLDPWODKLBJGODJRPTOGLBKDJPIGKREDIKSLSO

Gives:

ONEA CHIMNEY SIZING EXPERT
TWOA NATIVE TONGUE LAND OF BLUE LAGOON
THREEA ONE SQUARE FOUR TRIANGLES
ONED TINY IDEA BITS
TWOD CAPITAL SHORT DAY LONG
XXXXXXXXXXXXXXXX INTERSECTIONS ARE COMBO XX

These seem to be:

Clues for the crossword in BeastlyGerbil's image. ONEA is one across, ONED is one down.

Strangely:

The remaining text and the PAD are not the same length...

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    $\begingroup$ Ah I tried decrypting the other way round but didnt try that way :P Nice work!! I have no idea what that riddle means though $\endgroup$
    – Beastly Gerbil
    Jul 14, 2020 at 12:37
  • $\begingroup$ I commented this on the other answer too, bu to make sure you see it: I just realized that in all of my copy pasting, despite painstaking review, I missed one letter in the scrawl at the bottom. The updated is in the question. $\endgroup$
    – kristinalustig ♦
    Jul 14, 2020 at 14:34
  • $\begingroup$ @kristinalustig Thanks I figured something was up. $\endgroup$
    – LeppyR64
    Jul 14, 2020 at 14:58

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