Learn Hardcore Finnish: Minä pysyn puistossa suurin piirtein tunnin.

Emphasis / contrast
- Minä pysyn puistossa… = I (as opposed to someone else) will stay in the park…
  It can imply: You can go if you want, but I’m staying.
Clarity in learning materials
In textbooks and beginner contexts, Minä is often written to make it clear which person is meant.

So both are correct:

Pysyn puistossa suurin piirtein tunnin. (more neutral, typical)
Minä pysyn puistossa suurin piirtein tunnin. (a bit more emphatic or textbook-like)

Why is the verb in the present tense pysyn, even though the English translation uses “will stay”?

Finnish does not have a separate future tense. The present tense is used for:

things happening now
future plans and decisions, especially when there is a time expression

So:

Pysyn puistossa suurin piirtein tunnin.
→ in context usually means I will stay in the park for about an hour.

Contrast:

Pysyn puistossa joka päivä tunnin.
= I stay in the park for an hour every day. (habitual present)

The time expression (suurin piirtein tunnin) plus context tells you whether it’s about a current action, a habit, or a future plan.

What exactly does pysyä mean here, and how is it different from olla, jäädä, or viipyä?

pysyä means to stay / to remain (without leaving or changing state).

Minä pysyn puistossa… = I stay / I remain in the park… (I don’t leave)

Compared to similar verbs:

olla = to be
- Olen puistossa tunnin. = I am in the park for an hour.
  More neutral, just stating where you are.
jäädä = to stay, to remain, to be left behind / to end up
- Jään puistoon tunniksi. = I’ll stay in the park (instead of leaving).
  Often used at the moment of deciding not to leave.
viipyä = to stay / linger (emphasis on duration)
- Viivyn puistossa tunnin. = I’ll spend an hour in the park.

pysyä emphasizes not leaving / not moving away from the place or state you are already in.
olla is simpler and very common; your sentence would also be natural as:

Olen puistossa suurin piirtein tunnin.

Why is it puistossa and not something with a preposition like “in the park”?

Finnish mostly uses case endings instead of prepositions. Here:

puisto = park (basic form)
puisto + ssa → puistossa = in the park

-ssa / -ssä is the inessive case, meaning in(side) a place.

So:

puistossa = in the park
talossa = in the house
kaupassa = in the shop

English uses the separate word in; Finnish attaches the meaning to the noun.

What is the difference between puistossa, puistoon, and puistosta?

These are three different location cases:

puistossa – in the park (static location)
- Olen puistossa. = I am in the park.
puistoon – into the park / to the park (movement towards / into)
- Menen puistoon. = I go to the park.
puistosta – from the park / out of the park (movement away / out)
- Tulen puistosta. = I come from the park.

Your sentence uses puistossa because you are talking about staying at a place, not going to it or leaving it.

Could I move suurin piirtein tunnin to another place in the sentence, and would it change the meaning?

Yes, you can move it; the basic meaning stays the same, but the focus can shift slightly. All of these are grammatical:

Minä pysyn puistossa suurin piirtein tunnin. (neutral)
Minä pysyn suurin piirtein tunnin puistossa.
Suurin piirtein tunnin minä pysyn puistossa. (emphasis on the duration)
Puistossa pysyn suurin piirtein tunnin. (focus on in the park and its duration)

The most neutral, everyday version is the original order:

(Minä) pysyn puistossa suurin piirtein tunnin.

You almost never put suurin piirtein after tunnin alone (like tunnin suurin piirtein) in this kind of sentence; it sounds awkward.

What does suurin piirtein mean exactly, and are there simpler alternatives?

suurin piirtein literally means “roughly, approximately”, in the sense of more or less.

suurin piirtein tunnin ≈ for roughly an hour / about an hour

It is quite common, but slightly more informal/spoken-feeling than some other options. Very common alternatives:

noin tunnin – about an hour (very common, neutral)
suunnilleen tunnin – roughly an hour (close to suurin piirtein)
reilun tunnin – a bit more than an hour
vajaan tunnin – a bit less than an hour

So you could say, for example:

Pysyn puistossa noin tunnin.
Pysyn puistossa suunnilleen tunnin.

All would be natural.

Why is it tunnin instead of tunti or tuntia?

The base word is:

tunti = hour

Here we have:

tunnin = (for) an hour

This -n ending is the genitive / accusative singular, and it is commonly used for a single unit of measured duration:

Olen siellä tunnin. = I am there for an hour.
Odotan sinua tunnin. = I’ll wait for you for an hour.

You can think of it as a shortened form of:

yhden tunnin = one hour

Using tunti alone (without a case ending) in this position would be ungrammatical.
tuntia appears after numerals ≥ 2:

kaksi tuntia = two hours
kolme tuntia = three hours

But tuntia on its own is not used to mean for an hour; the natural form for for an hour is tunnin.

How is pysyn formed from pysyä, and how do I know which ending to use?

The verb’s basic (dictionary) form is:

pysyä = to stay / to remain

Finnish conjugates by adding personal endings to the verb stem.

Stem: pysy-

Present tense endings (indicative):

minä pysyn – I stay
sinä pysyt – you (sg) stay
hän pysyy – he/she stays
me pysymme – we stay
te pysytte – you (pl) stay
he pysyvät – they stay

So pysyn = pysy- (stem) + -n (1st person singular ending).

If you recognize the pattern, you can do the same with many other verbs ending in -yä / -yä:

näkyä → näyn, näyt, näkyy, näymme…
kypsyä → kypsyn, kypsyt, kypsyy, kypsymme…

Is there any difference in nuance between Minä pysyn puistossa suurin piirtein tunnin and a version with olla, like Minä olen puistossa suurin piirtein tunnin?

Both are grammatical and natural, but they feel a bit different:

Minä pysyn puistossa suurin piirtein tunnin.
Emphasis: I (am going to) stay / remain there and not leave for about an hour.
Slight nuance of remaining where I already am, or choosing not to move.
Minä olen puistossa suurin piirtein tunnin.
Emphasis: I will be in the park for about an hour.
More neutral; just states your location and its duration.

In everyday speech, many people would use olla unless they specifically want to highlight the idea of staying / not moving, but pysyä is perfectly normal too—especially in contexts like “Others may leave; I’ll stay (pysyä) in the park.”

Does this sentence sound natural in everyday spoken Finnish? How might a Finn actually say this?

Yes, it sounds natural. Some very typical spoken-style variants (depending on region and formality) are:

Mä oon puistossa noin tunnin.
Mä pysyn puistossa noin tunnin.
Pysyn puistossa varmaan tunnin verran.

Features you might hear in speech:

Mä instead of Minä
oon instead of olen
noin instead of suurin piirtein
extra words like varmaan (probably) or tunnin verran (for about an hour or so)

But your original sentence:

Minä pysyn puistossa suurin piirtein tunnin.

is correct and natural in neutral standard Finnish.