enigmatic puzzle - Treasure hunt 'round the world! (Interlude 2)

If you're interested in starting the treasure hunt from the very beginning, check out the prologue!

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Note: I fear I made these cities too obscure with my first riddle. The four unsolved cities have addenda added to them that should make them significantly easier to solve.

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Upon your arrival in Cambodia, you quickly notice that the entire airport is partitioned off, and tents line the gates and hallways. Looks like another interlude, you think to yourself. You notice that the number of tents here seems much smaller than the previous interlude, which is reassuring! You're getting to the end.

Noticing that the tents have name tags, you quickly find your own and enter it. Inside, you find bedding, a picture of your loved ones (weird), and an envelope. You know the drill. Time to open the next envelope.

Dear [insert username here],

Welcome to Cambodia! Since flights aren't departing here for the next 8 hours, you can feel free to grab some sleep. Or, you can choose to solve the simple, harmless puzzle on the back of this card. It's really up to you. At 0900, a concierge will present you with a ticket and you'll hop on a plane to your next destination! Oh, how wonderful. I'm getting the jitters.

Sleep tight! I'd say 'don't let the bedbugs bite', but I fear that ship might have sailed when we bought these tents in third-party bulk from offshore. Oh, well. I don't have to sleep in them!

Yours truly,

Bailey M
Puzzlemaster for the Treasure Hunt 'Round the World

P.S. The answer to the brainteaser will once again be a question. You will not receive your ticket tomorrow morning unless you are able to present the concierge with the aforementioned question. Good luck!

Luckily, you slept on the plane. Time to solve a puzzle. Flipping over the card, you read:

I planned a couple of trips awhile ago, but couldn't decide which one to take, so I ended up taking neither of them and feeling really bad about it. You can find details on my trips below. They were really cool, too!

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Trip 1

Coming from a town of few, I just can't wait to see
people! People! People! In increasing quantity!
I'm staying where I finish since it feels so right to me.

Trip 2

When I planned out this vacation, if only I knew;
bigger and bigger my target countries grew.
When I finish this trip, I'm going home, thank you.

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I can't remember my destinations, but I wrote out why I thought they were cool...anyways, here were the cities I was considering visiting. Maybe you can make some sense out of them.

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Destinations

The Avesta once noted that this city flows;
As their regime, here the terrible chose.
Now reborn anew, with haste this city grows.

A city of non-zero nuclear threat;
Elena is priced in at ten, I would bet.
For dry desert farming, it's the best you can get.

Through which both air and road transport passes,
Here announced the dawn of the era of the masses.

A festival city, yet not from Dubai;
Living history looms here as tall as the sky,
and it's nearly the finest if you're looking to buy.
The gateway of the north this came to be
In the land that stretches from sea to sea.

If you need an import, I'd hope there's no ice,
or enough for a truck to make one-way trips twice.
(Though Yamal is here in a pinch, which is nice.)

A birdlike creature, the foe of all snakes,
on this city's flag an appearance makes.
They have a whole castle for one man-made lake!

Home of the highlanders, a capital investment;
Most recently subjected to corruption's assessment.
Their country dissolved as a laughable contestant.
Stealing the title from the first month's river,
On Don Bosco's dream town, a new Marx delivered.

When flying, you'll land here, amidst ice and rocks.
When boating, the whole fjord is basically docks.

When driving, be careful you don't hit an ox.

Where once stood a church of good Lutheran grace,
a towering hotel now looms in its place.
(Some words here mean not what they say on their face.)
A unique reveal it used to be heard,
it looks like it sounds like the foot of a bird.

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P.S. I remembered that looking at a map with North America on the left and Eurasia on the right, none of my first trip went farther east than the westernmost point of my second trip. Don't know if that'll help, but it can't hurt, right? Anyways, good luck!

On the bottom of the page, scrawled in someone else's handwriting, you see:

poaxrhsirzzsyhfhrsyprozg? It's a Vigenere, which shouldn't shock you at this point.

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What question do you need to ask the concierge in the morning?

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Stanza-Specific Hints:

Stanza 1: Solved.
Stanza 2: Solved.

Stanza 3: Solved.
Stanza 4: Solved.
Stanza 5: Solved.
Stanza 6: Solved.
Stanza 7: Solved.
Stanza 8: Cryptic crossword.

Answer

A birdlike creature, the foe of all snakes,

on this city's flag an appearance makes.
They have a whole castle for one man-made lake!

This refers to Ulaanbaatar, the location of the Artificial Lake Castle. The city's flag shows Garuda, enemy of the Nagas.

If you need an import, I'd hope there's no ice,
or enough for a truck to make one-way trips twice.
(Though Yamal is here in a pinch, which is nice.)

This stanza describes Salekhard, which is located near the base of the Yamal Peninsula in Russia. Salekhard is on the opposite side of the Ob River from the highway, so it is only accessible by air or when there is no ice (so boats can cross the river) or when there is enough ice to drive across. Yamal Airlines operates out of Salekhard.

A festival city, yet not from Dubai;
Living history looms here as tall as the sky,
and it's nearly the finest if you're looking to buy.
The gateway of the north this came to be
In the land that stretches from sea to sea.

Edmonton is "Canada's festival city" (I found this before the extra lines were added, but didn't post it because I didn't see any connections to the second and third lines). It is also known as a "gateway to the north".

A city of non-zero nuclear threat;

Elena is priced in at ten, I would bet.
For dry desert farming, it's the best you can get.
Through which both air and road transport passes,
Here announced the dawn of the era of the masses.

Sabha, Libya, is where Muammar Gaddafi announced "the dawn of the era of the masses". It is the location of the Fort Elena castle, which is on Libya's 10 dinar note. It is also related to Libya's nuclear program.

Home of the highlanders, a capital investment;
Most recently subjected to corruption's assessment.
Their country dissolved as a laughable contestant.

Stealing the title from the first month's river,
On Don Bosco's dream town, a new Marx delivered.

The "first month's river" is Rio de Janeiro, which was the capital of Brazil before it was moved to Brasilia. Brasilia is located in the highlands of Brazil.

Lampost42 and Echo have found the other three cities, which are Kangerlussuaq, Kabul, and Tallinn.

Now we should try to determine what the trips were. If each trip had four cities, then the first trip visits Kangerlussuaq, Sabha, Edmonton, and Brasilia (ordered by increasing population), and the second visits Tallinn, Kabul, Ulaanbaatar, and Salekhard (ordered by increasing size of country), and then returns to Tallinn. When these are traced out on a map, they spell NO:

Using "NO" as the key for the Vigenere cipher reveals the question:

Can jet fuel melt steel beams?