Let's have a treasure hunt!

Question

What if I told you that I found a treasure, and that I'm willing to share it with you? Of course you'll have to go through an ugly, not even rhyming, riddle... But I know you're quite fond of them, so enjoy this one!

Make a 88 days round-trip
Go North, then West, enter a country
Between the sky and the sea, in the white horizon
Sum it in France, to the largest city
Name of a "pub maiden" (or something like that), go to her fathers' home
In their most known body of water
Keep only the name, in an obvious code
Dash South and point toward the East from California
But stop a bit sooner to avoid the cops!
Under the anchor, remove the circle and circle 7 times
One animal lead to another, through the cosmic clouds
Append his french cousin (because we need a key!)
Finally remove xbviilps, and get your reward.

Will you find the treasure?

Hint 1:

The riddle is sequential: every line is a step toward the other. As such, teamwork may be useful if you share your findings ;)

Hint 2:

Since the "sum it in France" line seems problematic : when I talk about a sum, I expect a number. Also, forget Paris.

Hint 3:

Here are the themes for each line (in the wrong order of course), except for 2 lines being part of the same step, and 2 other lines having two (close) steps (and thus 2 themes): Astronomy, Astronomy, Communications, Cryptography, Cryptography, Geography, Geography, Geography, Music, Language, Physics, Physics, Vexillology, Vexillology
Have fun with this!

Answer 1

[I'm making this a Community wiki -- it seems better suited to attacking this puzzle piece by piece, because all edits take part in one place. I've taken some insights from other answers, especially from Joey Dionne's. Consider upvoting them.]

After much hunting, we've found the treasure. It is ...

... Friendship.

Make a 88 days round-trip

(Astronomy) Mercury's orbit around the sun is 88 days.
(Physics) Mercury is also an element with symbol Hg.

Go North, then West, enter a country

Up and left from Hg in the Periodic table of elements is Silver.
(Geography) Argentina is an artificial name derived from the Latin name o fsilver (La Plata).

Between the sky and the sea, in the white horizon

(Vexillology) Argentina's flag has a three horizontal stripes: Light blue (sky), white (horizon) and light blue again (sea). In the centre is the sun of May.

Sum it in France, to the largest city

(Cryptography) The A-to-Z sum of sun is 54: S (19) + U (21) + N (14)
(Geography) In France, the départements are numbered. Number 54 is Meurthe-et-Moselle, whose capital and largest city is Nancy.

Name of a "pub maiden" (or something like that), go to her fathers' home

(Music) "Nancy the tavern wench" is a song by the Scottish pirate metal band Alestorm, which hails from Perth, Scotland.

In their most known body of water

(Geography) Scotland's most notorious body of water surely is Loch Ness.

Keep only the name, in an obvious code

(Communications) Loch means Lake in Scottish, so the name proper is just Ness. I'm not sure it's an "obvious" code, but in Morse, it's -. . ... ..., that is a dash followed by eight dots.

Dash South and point toward the East from California

(Physics) Take the name in Morse as directions in the periodic system of elements: A dash means move down; a dot means move east. Start in "California", CA, that is at Calcium, Ca.

But stop a bit sooner to avoid the cops!

Moving the full 1 south and 8 east would land us as Pd (Palladium), but we want to avoid the cops (or in other words, the Police Department, PD), so we stop at Rhodium, Rh.

Under the anchor, remove the circle and circle 7 times

(Vexillology) The state flag of Rhode Island has an anchor surrouned by a circle of thirteen golden stars. But we must remove the circle under the anchor. Right under the anchor on a ribbon is the state's motto, HOPE. Remove the O to get HPE and then Caesar-shift seven times to get an animal, namely an Owl.

One animal lead to another, through the cosmic clouds

(Astronomy) The Owl nebula is a "cosmic cloud" in the constallation Ursa Major, the Great Bear.

Append his french cousin (because we need a key!)

(Language) The bear's French cousin is probably just its name in French, ours.

Finally remove xbviilps, and get your reward.

(Cryptography) We have an eight-letter key, bearours, and an eight-letter ciphertext, xbviilps, which we need to "remove". If we decrypt that with Vigenère, which kinda removes the letter codes from each other, we get "edfjgjca".

These letters are all from the beginning of the alphabet and we can turn them into a number by substituting a with 0, b with 1, ..., j with 9, and we get 43596920. This number can be read as latitude and longitude in degrees and minutes. One of the possibilities is 43° 59' N, 69° 20' W, which leads to a town in Maine called Friendship.

Used fields according to Hint 3:

Astronomy (Mercury)
Astronomy (Owl Nebula)
Communications (Morse code)
Cryptography (AZ sum)
Cryptography (Vigenère)
Geography (Argentina)
Geography (Nancy)
Geography (Loch Ness)
Music (Alestorm)
Language (Bear → Ours)
Physics (Mercury, Silver)
Physics (Calcium, Rhodium)
Vexillology (Sun of May)
Vexillology ("Hope")

Answer 2

Partial Answer

Make a 88 days round-trip

Mercury's year round trip around the sun last 88 days

Go North, then West, enter a country

The element north west of mercury in the periodic table is silver. The country we enter is Argentina, because in Italian it means "made of silver, silver colored"

Between the sky and the sea, in the white horizon

The argentinian flag is three horizontal stripes: blue(sea), white (horizon) and blue(sky). Inside the white stripe is a Sun

Sum it in France, to the largest city

From @MOehm

To "sum it in France" could mean the A-Z sum of SUN, 54, and reading it as the number of a department, which leads to the city of Nancy

Name of a "pub maiden" (or something like that), go to her fathers' home

Nancy, the only girl in the Oliver Twist gang, is a prostitute (loose definition of a "pub maiden"). Her "father", Charles Dickens is English and now we are in England

In their most known body of water

The most known english body of water is the English Channel.

Keep only the name, in an obvious code

The English Channel is a sea and SEA is the airport code of Seattle

Dash South and point toward the East from California
But stop a bit sooner to avoid the cops!

From there I guess we head south of Seattle and somewhere in California we go east, stopping before Beverly Hills (cop) so maybe Bel Air?

Under the anchor, remove the circle and circle 7 times
One animal lead to another, through the cosmic clouds
Append his french cousin (because we need a key!)
Finally remove xbviilps, and get your reward.

Answer 3

Partial answer:

Make a 88 days round-trip

Mercury's year round trip around the sun last 88 days (Credit to Joey Dionne)

Go North, then West, enter a country

Starting at Mercury (Nevada), heading north puts you the Canadian border, West takes you to Russia

Notes:

#2 states Go North (by an unspecified amount), so Japan is an option, as is America (Alaska) if you entered Canada while going North.

Answer 4

Snippets of information:

There was a book called 88 Days to Kandahar: A CIA Diary by Robert L. Grenier.

Kandahar is located in Afghanistan, which is located in the Middle East (could it be a reference to the directions)

There is another book written called White Horizon: The Arctic in the Nineteenth-Century British Imagination

The largest city in France is Paris. I'm taking things way too literally sighhhhhhhhhh