Learn Hardcore Finnish: Minusta lukeminen illalla on rentouttavaa. - In my opinion reading in the evening is relaxing.

So here minusta does not really mean physical movement “from me”; it marks whose opinion or feeling is being expressed. The same pattern works with other persons:

Sinusta tämä on tylsää. – “You think this is boring.”
Heistä elokuvat ovat kiinnostavia. – “They think movies are interesting.”

What’s the difference between minusta and minun mielestäni?

Both mean almost exactly the same: “in my opinion”.

Minusta lukeminen illalla on rentouttavaa.
Minun mielestäni lukeminen illalla on rentouttavaa.

Nuance:

minusta – shorter, very common in everyday speech and writing.
minun mielestäni – a bit longer and slightly more explicit/emphatic (“in my view / in my mind”), sometimes felt a little more formal or careful, but still perfectly normal in casual speech.

In most contexts you can freely choose either one.

Why is it lukeminen and not the verb lukea?

Lukea is the basic verb “to read”.
Lukeminen is a noun derived from that verb: “reading” (the activity).

Finnish usually uses this -minen noun when a verb idea acts as the subject of the sentence:

Lukeminen illalla on rentouttavaa.
“Reading in the evening is relaxing.”

This is parallel to English using a gerund:

“Reading in the evening is relaxing.” (not usually “To read in the evening is relaxing.”)

How -minen works (briefly):

take the verb stem: luke-
add -minen → lukeminen = “reading”

Some more examples:

uida → uiminen – swimming
Uiminen on hauskaa. – “Swimming is fun.”
opiskella → opiskelu / opiskeleminen – studying
Opiskelu on raskasta. – “Studying is tiring.”

So in this sentence, lukeminen is a regular noun functioning as the subject.

What form is rentouttavaa, and why isn’t it just rentouttava?

Rentouttava is the basic form of the adjective “relaxing”.

In the sentence we see rentouttavaa, which is:

rentouttava = relaxing (nominative)
rentouttavaa = relaxing (partitive singular)

Here it is a predicative adjective (the thing that comes after on “is”) and it’s in the partitive. This is very typical when:

the subject is an uncountable or abstract noun used in a general sense.

Compare:

Suklaa on hyvää. – “Chocolate is good.”
Vesi on kylmää. – “The water is cold.”
Maito on kallista. – “Milk is expensive.”

In all these, the subject is a kind of “mass” or general concept, and the adjective is in the partitive: hyvää, kylmää, kallista.

Lukeminen (“reading”) is also seen as an abstract activity, like a mass noun, so Finnish treats it the same way:

Lukeminen illalla on rentouttavaa. – “Reading in the evening is relaxing.”

Using rentouttava (nominative) here would sound unnatural; Finnish speakers strongly prefer the partitive form in this kind of general statement.

Would Lukeminen illalla on rentouttava be wrong?

It’s not strictly impossible, but to a native speaker it sounds off or incomplete in this context.

Lukeminen illalla on rentouttavaa.
is the normal, natural way to say “Reading in the evening is relaxing” as a general statement.

If you use rentouttava in the nominative, you almost always expect a noun after it:

Lukeminen illalla on rentouttava harrastus.
“Reading in the evening is a relaxing hobby.”

Here rentouttava agrees with harrastus (a countable noun), so nominative is fine.

But with bare lukeminen as a general abstract subject, native speakers choose rentouttavaa.

What case is illalla, and how does it work as a time expression?

Illalla is:

base noun: ilta = evening
case: adessive singular → illalla = “in the evening, at evening-time”

Finnish often uses the adessive to talk about parts of the day:

aamu → aamulla – in the morning
päivä → päivällä – in the daytime / during the day
ilta → illalla – in the evening
yö → yöllä – at night

So:

Lukeminen illalla on rentouttavaa.
= “Reading in the evening is relaxing.”

Note that:

illalla can mean “(on) this evening / that evening” in a concrete context:
Mennään illalla elokuviin. – “Let’s go to the movies this evening.”
in a general statement like your sentence, it’s more “at (the) evening time” in general.

There is also iltaisin = “in the evenings / in the evenings habitually”:

Luen iltaisin. – “I read in the evenings (as a habit).”

Both illalla and iltaisin can be used in generalizations, but illalla is perfectly fine here.

Can the word order change, for example: Illalla lukeminen on minusta rentouttavaa?

Yes. Finnish word order is quite flexible, and all of these are grammatically fine:

Minusta lukeminen illalla on rentouttavaa.
Lukeminen illalla on minusta rentouttavaa.
Illalla lukeminen on minusta rentouttavaa.

The differences are about emphasis and information structure, not basic meaning.

Rough tendencies:

Starting with Minusta highlights that you are giving your opinion.
Starting with Lukeminen illalla highlights the activity/time first.
Starting with Illalla might connect better to what was said before about evenings.

In everyday speech, Minusta lukeminen illalla on rentouttavaa and Lukeminen illalla on minusta rentouttavaa are probably the most typical.

Could I also say On rentouttavaa lukea illalla? How does that compare?

Yes, that’s another very natural way to say it:

Minusta on rentouttavaa lukea illalla.
≈ “I find it relaxing to read in the evening.”

Here the structure is:

on rentouttavaa – “it is relaxing”
lukea – infinitive “to read”
illalla – in the evening

English also often uses this type of impersonal structure: “It is relaxing to read in the evening.”

So you have two common options:

Minusta lukeminen illalla on rentouttavaa.
(using the noun lukeminen as subject)
Minusta on rentouttavaa lukea illalla.
(using the infinitive lukea after the adjective)

Both are idiomatic; (2) sounds slightly more like the English “It’s relaxing to read in the evening.”

Does this sentence mean “I like reading in the evening”? If not, how would I say that?

The given sentence expresses an opinion about how something is:

Minusta lukeminen illalla on rentouttavaa.
“In my opinion, reading in the evening is relaxing.” / “I find reading in the evening relaxing.”

It doesn’t directly say that you like it (though it obviously suggests you might).

To say “I like reading in the evening” more directly, you would typically use pitää or tykätä:

With pitää
- -sta/-stä:
- Pidän lukemisesta illalla.
  “I like reading in the evening.”
  (literally “I like of reading in the evening.”)
With tykätä (more colloquial) + -sta/-stä:
- Tykkään lukea illalla.
  “I like to read in the evening.”

So:

Minusta lukeminen illalla on rentouttavaa. = opinion about its quality (relaxing)
Pidän lukemisesta illalla. / Tykkään lukea illalla. = directly expressing that you enjoy it.