Learn Hardcore Finnish: Kesällä menemme laivalla pienelle saarelle viikonlopuksi. - In the summer we go by ship to a small island for the weekend.

The adessive case (-lla / -llä) often means “on / at” in a physical sense (pöydällä = “on the table”), but it’s also commonly used for time expressions, especially:

seasons: kesällä (in summer), talvella (in winter)
parts of the day: aamulla (in the morning), yöllä (at night)

So Kesällä literally is “at summer / on summer”, but idiomatically it means “in (the) summer.”
You can’t say just kesä menemme… – you need a case ending to show the time role.

Could I also say Kesällä me menemme...? Do I need the pronoun me?

Both are correct:

Kesällä menemme laivalla…
Kesällä me menemme laivalla…

Finnish usually drops subject pronouns, because the verb ending already shows the person:

menemme = “we go” (1st person plural)

You use me mainly for emphasis or contrast, e.g.:

Me menemme laivalla, mutta he menevät autolla.
“We go by boat, but they go by car.”

In a neutral sentence like yours, leaving me out is the most natural.

Does menemme mean “we go” or “we will go”? How is the future expressed?

Menemme is the present tense form of mennä “to go”, 1st person plural:

me menemme = “we go / we are going”

Finnish doesn’t have a separate future tense. The present tense covers both present and future, and context tells you which is meant:

Nyt menemme saarelle. – “Now we are going to the island.”
Kesällä menemme saarelle. – “In the summer we will go to the island.”

So here menemme is naturally understood as “we will go” because of Kesällä.

Why is it laivalla and not something like laivassa? How does Finnish say “by boat”?

The base word is laiva “ship / large boat”.

laivalla = laiva
- -lla (adessive)
laivassa = laiva
- -ssa (inessive)

In expressions of means of transport, Finnish usually uses the adessive (-lla / -llä):

laivalla – by boat/ship
autolla – by car
bussilla – by bus
junalla – by train
pyörällä – by bike

So laivalla here means “by boat / by ship”.

Laivassa would literally mean “inside the boat / on the ship”, describing location, not means, e.g.:

Olemme laivassa. – “We are on the ship.”

Why do both words pienelle saarelle have the -lle ending? Isn’t that redundant?

In Finnish, adjectives agree with the noun they modify in:

number (singular/plural)
case (nominative, allative, etc.)

Base forms:

pieni – small
saari – island

Here we use the allative case (-lle) to show movement to / onto a place:

pienelle = pieni + lle
saarelle = saari + lle

Because pieni describes saari, it must match the noun:

pienelle saarelle = “to (a) small island”

This “double ending” is normal and required in Finnish; it’s how you know which words belong together.

Why is it saarelle and not saareen? What’s the difference between these two “to the island” forms?

Both are possible forms of saari “island”:

saarelle = allative (-lle) → “to/onto the island (as a surface/area)”
saareen = illative (-Vn) → “into the island (into the inside)”

In practice:

For islands, saarelle is the most natural and common; you’re going onto the island as a place/surface.
Saareen is grammatically correct but feels more like going into the interior of something, which is less natural for islands as general locations.

So native speakers almost always say:

mennä saarelle – “go to the island”

That’s why your sentence uses saarelle, not saareen.

What exactly does viikonlopuksi mean, and what does the ending -ksi do?

The base word is viikonloppu “weekend”.

viikonlopuksi = viikonloppu
- -ksi (translative case)

The translative (-ksi) has several uses; one of them is to express duration or “for (a period of time)”:

kahdeksi viikoksi – for two weeks
päiväksi – for (one) day
viikonlopuksi – for the weekend

So viikonlopuksi here means “for the weekend” (i.e. we go there and stay for the duration of a weekend).

Compare with:

viikonloppuna (essive) – “on/over the weekend” (when something happens)

Your sentence is about how long you go there, so viikonlopuksi is used.

Can you give a word-for-word breakdown of the whole sentence?

Yes. Sentence:

Kesällä menemme laivalla pienelle saarelle viikonlopuksi.

Word-by-word:

Kesällä – in summer (kesä + llä, “at/on summer”)
menemme – we go / we will go (present tense of mennä, 1st person plural)
laivalla – by boat/ship (laiva + lla, by means of transport)
pienelle – to a small (pieni + lle, allative, agreeing with saarelle)
saarelle – to the island (saari + lle, allative)
viikonlopuksi – for the weekend (viikonloppu + ksi, translative “for (a duration)”)

Natural English: “In the summer, we go by boat to a small island for the weekend.”

Can I change the word order, for example: Menemme kesällä pienelle saarelle laivalla viikonlopuksi? Does it sound natural?

Yes, Finnish word order is quite flexible, and your version is grammatically fine:

Kesällä menemme laivalla pienelle saarelle viikonlopuksi.
Menemme kesällä laivalla pienelle saarelle viikonlopuksi.
Menemme kesällä pienelle saarelle laivalla viikonlopuksi.

All of these are understandable and acceptable.

Typically:

Time expressions (like Kesällä) often come early in the sentence.
Putting Kesällä first slightly emphasizes the time (“As for the summer, that’s when we go…”).
Moving words around can shift emphasis or focus, but in neutral speech all of the above orders are fine.

So yes, your alternative is okay, just a bit different in rhythm and emphasis.

Could I say Kesällä menemme veneellä instead of laivalla? What’s the difference between vene and laiva?

You can, but it changes the nuance:

laiva – “ship”, typically a larger vessel (ferry, cruise ship, cargo ship)
vene – “boat”, usually smaller (rowing boat, motor boat, sailing boat)

So:

menemme laivalla – we go by ship (sounds like a ferry/cruise-type vessel)
menemme veneellä – we go by (small) boat

Both use the same adessive case:

laivalla, veneellä = “by ship”, “by boat”

Which one you choose depends simply on what kind of craft you’re actually using.