Matkan jälkeen olen yleensä väsynyt, mutta tällä kertaa olin iloisesti yllättynyt siitä, kuinka rauhallisesti kaikki sujui.

Because jälkeen is a postposition. In Finnish, postpositions come after the noun phrase they belong to.

So:

• matkan = trip/journey in the genitive
• jälkeen = after

Together, matkan jälkeen means after the trip/journey.

A native English speaker often expects a preposition first, but Finnish often uses postpositions instead.

Because jälkeen requires the word before it to be in the genitive.

So:

• matka = trip, journey
• matkan = of the trip / trip in the genitive
• matkan jälkeen = after the trip

This is just part of the grammar of the postposition jälkeen. Different postpositions and prepositions require different cases.

Finnish has no articles, so it does not have separate words for a/an or the.

That means matkan jälkeen can be understood as:

• after the trip
• after a trip
• sometimes more generally after travelling

The exact meaning depends on context. English forces you to choose an article, but Finnish usually does not.

Because the sentence contrasts:

• a usual/general situation → olen yleensä väsynyt
• one specific past occasion → tällä kertaa olin iloisesti yllättynyt

So:

• olen = present tense, used for what is generally true
• olin = past tense, used for what happened that one time

This is very natural in Finnish. The word yleensä strongly suggests a general habit, while tällä kertaa points to a particular occasion.

Tällä kertaa means this time or on this occasion.

It is a very common expression. The forms are:

• tällä = adessive form of tämä
• kertaa = partitive of kerta

As a learner, it is best to remember tällä kertaa as a fixed phrase meaning this time.

Related expressions:

• sillä kertaa = that time / on that occasion
• ensi kerralla = next time
• viime kerralla = last time

They are forms that originally come from verbs, but in sentences like this they behave much like adjectives.

• väsynyt comes from väsyä = to get tired
• yllättynyt comes from yllättyä = to be surprised

With olla, they describe a state:

• olen väsynyt = I am tired
• olin yllättynyt = I was surprised

So even though these forms are historically participles, a learner can often treat them like adjectives in everyday use.

Because iloisesti is an adverb, and here it modifies yllättynyt.

• iloinen = happy, joyful
• iloisesti = happily, joyfully

In this sentence, iloisesti yllättynyt means something like pleasantly surprised or gladly surprised, not that the speaker was simply a happy person.

Finnish often uses an adverb in places where English uses an expression like pleasantly surprised.

Because yllättyä normally takes the case pattern jostakin = to be surprised at/about something.

So:

• siitä is the elative form of se
• yllättynyt siitä = surprised by that / surprised about that

After siitä, the sentence explains what that that is:

• kuinka rauhallisesti kaikki sujui

So the structure is roughly:

• I was pleasantly surprised by the fact that / by how ...

In English, you might not always need a word like that, but in Finnish this kind of pronoun + clause structure is very common.

Here kuinka means how.

So kuinka rauhallisesti kaikki sujui means how calmly / how smoothly everything went.

In many situations, kuinka and miten can both mean how. But there can be small differences in style:

• kuinka can sound a bit more formal, literary, or emphatic
• miten is often more neutral in everyday speech

In this sentence, kuinka works very naturally.

Because the word is modifying a verb, not a noun.

• rauhallinen = calm, peaceful → adjective
• rauhallisesti = calmly, peacefully → adverb

Here it describes how everything went:

• kaikki sujui rauhallisesti

So Finnish needs the adverb form rauhallisesti.

Sujui is the past tense of sujua.

• sujua = to go, proceed, run, turn out
• sujui = went, proceeded, turned out

This verb is very common in expressions like:

• Kaikki sujui hyvin. = Everything went well.
• Miten matka sujui? = How did the trip go?

In this sentence, sujui suggests that things proceeded smoothly and without problems.

Because here kaikki means everything, which is treated as a single whole.

So:

• kaikki sujui = everything went well

Even though kaikki can sometimes refer to all people or all things, in this kind of sentence it acts like everything, so the verb is singular.

Because kuinka rauhallisesti kaikki sujui is a subordinate clause, and Finnish normally separates subordinate clauses with a comma.

So the structure is:

• main clause: olin iloisesti yllättynyt siitä
• subordinate clause: kuinka rauhallisesti kaikki sujui

Finnish comma use is often a bit more regular here than English.

Yes, Finnish word order is fairly flexible, although different orders can sound more or less natural depending on emphasis.

For example, these are possible with slightly different focus:

• Matkan jälkeen olen yleensä väsynyt.
• Yleensä olen matkan jälkeen väsynyt.
• Olen yleensä matkan jälkeen väsynyt.

The original sentence starts with Matkan jälkeen to set the scene first: after a trip. That is a very natural choice.

Finnish word order often reflects information structure and emphasis more than strict fixed position rules.