# Travelling the world

Yesterday, I received a text message from one of my best friends:

This is great, Ryan. This trip is so wonderful, best day ever dude! Wow!

Well, I guess he's having fun right now while I'm sitting at my desk, working... I was curious to know more about his trip (offered by his parents, the dude's been gone for 3 months now), and of course what countries or cities he had visited. This was his answer:

You may think that travelling is easy
But I had to make it through security
Not one nor two, but eighteen times!
I tell you, it's you who'll get the primes...
Forget it, most important thing is to get some sleep
Or else it would have felt like wasting my youth!
Don't focus on the rhymes, they're not so deep,
Concentrate on the list you'll find, here lies the truth.

Can you help me find out what these lines mean, and where my friend has been this whole time?

Hint:

The steganography tag is for the first text message. The riddle is here to help you find out what the message hides.

Hint 2:

Apparently, my friend hid the countries/cities he visited in the first text message only! How can it be?

The text message is very short and yet contains a steganographically hidden message, so presumably the solution involves manipulation of individual letters rather than words.

But I had to make it through security
Not one nor two, but eighteen times!

The number of letters in the text message is exactly $3\times18$, so we can split it up into eighteen three-letter strings. Three-letter strings could be interpreted as airport codes - this would explain why your friend had to pass through security eighteen times, once for each of these airports.

THI
SIS
GRE
ATR
YAN
THI
STR
IPI
SSO
WON
DER
FUL
BES
TDA
YEV
ERD
UDE
WOW

I tell you, it's you who'll get the primes...

Let's try choosing just the primes-numbered airports from the above list; perhaps this shorter list is of the places he's actually been.

The 2nd is SIS - Sishen, South Africa.
The 3rd is GRE - Greenville Municipal Airport, USA.
The 5th is YAN - Yangambi, DR Congo.
The 7th is STR - Stuttgart, Germany.
The 11th is DER - Derim, Papua New Guinea.
The 13th is BES - Brest, France.
The 17th is UDE - Uden, Netherlands.

But I had to make it through security
Not one nor two, but eighteen times!

It's surely significant that the number of letters in the text message is exactly $3\times18$, or $4\times18$ if we count spaces and punctuation. The first thing that springs to mind is considering every 3rd letter (or every 4th character, counting spaces and punctuation), but these give respectively:

ISERNIRIONRLSAVDEW
S AR.IRIONF TYEU !

... neither of which seems to make much sense.

I tell you, it's you who'll get the primes...

This seems to suggest taking all the letters/characters in prime-numbered positions. But applying this to the original message, either ignoring or counting spaces and punctuation, gives:

HIIGTYHSPOOUSDVE
HI SETYNHI DR, VREO

... and applying it to the 18-length strings we already found gives respectively:
SENRRSE
A.RFT

None of these results really makes much sense as it stands, but maybe one of them is close to something that does?

• 3x18 is a good start. But what can you do with this information? Look at the new hint :) – IAmInPLS Nov 20 '16 at 10:44
• @IAmInPLS I have a new idea, but it might be a bit tenuous ... airport codes? – Rand al'Thor Nov 20 '16 at 12:42
• @IAmInPLS See edit :-) – Rand al'Thor Nov 20 '16 at 12:50
• Nice! This is it. Passing eighteen times through security was a hint for the numbers of letters and that the things you'll find would be airports. – IAmInPLS Nov 21 '16 at 9:08
• @IAmInPLS Wait, Ulan-Ude is actually UUD ... I can't find an airport with code UDE :-/ – Rand al'Thor Nov 21 '16 at 12:10

It seems to me

There is a word in each line of the riddle which is a synonym.

So

1. Travelling - Trip
2. Looking at second line
3. Times - Day
4. Primes - Best
5. Important - Great
6. Looking at sixth line
7. Looking at seventh line
8. Looking at eighth line

• The riddle is related to travelling, but you are way off! I'll add a hint :) – IAmInPLS Nov 20 '16 at 10:43