More than surprising,
and slippery to the core,
I give resistance.
I hide my secrets,
until you come upon me,
revealing myself.
Evening stars of,
transcendental quality,
illuminate me.
Unravelling the,
centrally coiled hemisphere,
signifying me.
The source of gold eggs,
sifting sibilant language,
giving birth to me.
I'm from the third sphere,
said the Swiss eponymous,
for my sixth one.
Perhaps you are a
SPOILER.
The giveaway (if this is right) was actually Tom's comment that
"an anagram of the answer gives someone who could be a Knight from the relevant country"
because that suggested
looking for anagrams of SIR POLE.
Anyway, here are explanations of the verses (some with thanks to Tom for providing pointers in comments to things I'd missed; I'm leaving in my own half-baked thoughts even where they were wrong).
More than surprising,
and slippery to the core,
I give resistance.
A spoiler gives away the otherwise surprising plot of a book or movie. At the centre of "spoiler" we find oil, which is slippery. A spoiler on a car provides resistance to airflow and hence turbulent rather than laminar flow in a particular region, which reduces overall drag by some means I don't understand. Edited to add: OP indicates that I'm misunderstanding the first line and need to "translate symbolically", and after further prodding I finally get it: it's a reference to the SO markup for spoilers,
>!. So>is "more than" and!is "surprising".
I hide my secrets,
until you come upon me,
revealing myself.
This would apply pretty well to book/movie spoilers, but I think it's actually referring to the spoiler-hiding mechanism we have here. Spoilering a paragraph like this one you're reading right now hides its secrets but when you move your cursor over it it reveals itself.
Evening stars of,
transcendental quality,
illuminate me.
Currently baffled by this. Does "transcendental" refer to transcendental numbers? (See the sixth verse, below.) Perhaps -- though this is rather a stretch -- we're taking the middle of Hesperus (Venus as the "evening star") and inserting "oil" (as in an illuminating oil lamp) to yield SPOILER. But what's transcendental about that? And why "evening stars", plural, in that case? And why only the middle of "Hesperus"? I think it's just coincidence that this construction works. Edited to add: yes, it's coincidence; OP's intention was that "evening stars" indicates evenly spaced letters: SPOILER yielding PI and E or $\pi$ and $e$, both transcendental.
Unravelling the,
centrally coiled hemisphere,
signifying me.
SPOILER is almost an anagram of (found by unravelling) the central letters of "coiled" and "hemisphere". Perhaps "centrally" is referring to itself too, which would give us the missing "r". Edited to add: OP indicates that the actual intention was OILE from "centrally coiled" plus SPR from "hemisphere" (i.e., half of SPHERE).
The source of gold eggs,
sifting sibilant language,
giving birth to me.
Currently baffled by this. The story of the goose that laid golden eggs is first found in Aesop, whose name has a lot of letters in common with SPOILER, but I don't see how to do anything useful with that. And "goose" in French is "oie" which also has a lot of letters in common with SPOILER, but I don't see what to do with that either. Edited to add: OP indicates that "a source of gold or eggs" might have been a better L1 and that we're looking for a computer language here, and after a bit more prompting from OP because I was stupid this is of course ORE/ROE plus LISP.
I'm from the third sphere,
said the Swiss eponymous,
for my sixth one.
Sixth letter is E, so maybe this is a reference to the transcendental number e, named for the Swiss mathematician Euler. Not sure about the "third sphere"; perhaps there's some fanciful remark Euler made about e. (I guess it's the third celestial sphere, though what that is depends on whose geocentric model you use and whether you count from the inside or the outside.) Edited to add: nope, that's all wrong; OP indicates that actually "the third sphere" = 1/3 of SPHERE = SP, plus "said the Swiss eponymous" = sounds-like a Swiss person after whom things are named = sounds-like Euler = OILER.
Maybe it's
Electricity
More than surprising
Electricity can give you a shock
Slippery to the core
Electricity flows and has current
I give resistance.
Electrical resistance
I hide my secrets
You can't see electricity
until you come upon me, revealing myself.
But you can see its effects when you switch appliances on.
Not sure about the connection to the title,
but remove the elec and Tricity is in Gdańsk.
Are you :
A snail?
More than surprising, and slippery to the core, I give resistance.
The shell is resistant, but the animal is slippery inside. Plus this is a surprising animal.
I hide my secrets, until you come upon me, revealing myself.
Noone know what is in a snail shell, until you pick it up and look inside.
Plus for the title
This city, Gdansk (title) kinda looks like a snail upside down, and the knight might refer to snail horns.
This answer is densa approved :D
For the first two parts, it would nicely match any
Carnivorous plant
But the third part is not explained. Note that
Transcendental probably refers to transcendental numbers such as $\pi$, but I can't find anything else related to numbers here.
Old answer
Maybe
Quicksand
More than surprising, and slippery to the core, I give resistance.
Definitely surprising, slippery when trod upon, and you won't let me go
I hide my secrets, until you come upon me, revealing myself.
I can't tell until I'm stuck in there
I can't explain the title though.
Partial Answer: Are you
the Moon
More than surprising,
Not sure on this one
and slippery to the core,
Moon rock is an excellent lubricant
I give resistance.
Not sure here either
I hide my secrets, until you come upon me, revealing myself.
Dark Side of the Moon isn't visible from Earth, so we didn't know what was up there until we landed there and got to see it for ourselves
Evening stars of, transcendental quality, illuminate me.
The Moon appears luminous due to reflected sunlight.
I have a meaning the the part that @fffred lacks. I think it could be:
your mirror image
I hide my secrets, until you come upon me, revealing myself.
the mirror itself doesn't show much, until you stand in front of it revealing your own image.
Guess we can combine this wif @fffred's answer to make a...
sand mirror? :D
EDIT: Could it be...
The sunset, night? Hides stars, moon, and planets (evening stars) until it's time for it. OR even...DARKNESS/Light? which hides things until light comes
FINAL EDIT: gonna give up if I don't get it right this time, after having read a bit about Gdansk history :D
Castle, fortress, city-walls or the fortress door, because...
They give ressitance againts enemies. Hide the city secrets, until you traspass them. For the location of the city, it might have some good starts illumination (I guess). You can hide yourself when desired, is conected with the Teutonic Knights who tried to invade the city...
How About:
Diamond
More than surprising, and slippery to the core, I give resistance.
Diamonds are great electrical insulator, the carbon making up a diamond can also be slippery when in Graphite form
I hide my secrets, until you come upon me, revealing myself
Diamonds are hidden deep in the Earth, and need to be mined to be revealed
Evening stars of, transcendental quality, illuminate me.
Diamonds are checked for impurities
From the comment made by @Tom on the question
The tags all started with letters that could spell out HARD, and diamond is one of the hardest natural materials
Fireflies
More than surprising, and slippery to the core, I give resistance.
The bugs are slippery when squashed
I hide my secrets, until you come upon me, revealing myself
At night, they are hard to see until the light is turned on, or revealed
Evening stars of, transcendental quality, illuminate me.
The lights can be thought of like little stars in the night
To explain the "dancing night"
The fireflys dance and illuminate their lights at night
Could it be
Glass
More than surprising, and slippery to the core, I give resistance.
Things will slide on glass when you don't expect it (black ice is like glass), and electricity will not flow through glass.
I hide my secrets, until you come upon me, revealing myself
Glass is see through, hidden, until you run into it, then you know its there
Is it just
Euler?
Verse 1
Slippery to the core: Euler is said like "oiler"
I give resistance: Euler wrote several formulae on fluid dynamics (which would deal with resistence)
Verse 2
Not sure
Verse 3
Transcendental numbers $\pi$ and $e$ are used in Euler's identity, and Euler worked with $e$ quite a bit in general (which is why it's known as Euler's number, though he didn't discover it).
Verse 4
This fits Euler spiral pretty well, though I'm not sure they're hemispheres.
Verse 5
Russia was the source of Fabergé eggs, and Russian is a more sibilant language than most (having three or four sibilant sounds vs. most which have two, though one did/does have 27) and Euler attended a Russian academy, helping "give birth" to his mathematical intuition. He also continued to live there, apparently, until his death).
Verse 6
Your sixth verse mentions being from Earth, the third "sphere" (rock, anybody?) from the sun, and Euler is Swiss, and though Swiss isn't a language, Euler is a swiss name
