Due escursionisti controllano il dislivello e l'altitudine.

Due escursionisti simply means two hikers / two excursionists.

In Italian, a number can directly come before a noun without an article:

• due escursionisti = two hikers
• tre amici = three friends
• quattro case = four houses

If you say i due escursionisti, that means the two hikers specifically. So the article adds definiteness, just like the in English.

In your sentence, due escursionisti is an indefinite subject: just two hikers, not necessarily the two hikers.

Escursionisti is the plural of escursionista, a noun meaning hiker, excursionist, or someone who goes on outings or hikes.

A useful detail: nouns ending in -ista can be masculine or feminine in the singular, depending on the person:

• l'escursionista = the hiker (male or female, depending on context)

In the plural, the endings change:

• escursionisti = masculine plural
• escursioniste = feminine plural

So due escursionisti usually means:

• two male hikers, or
• a mixed group including at least one male

If the group were two women, you would normally say due escursioniste.

Controllano is the third person plural of controllare in the present indicative.

The verb matches the subject:

• io controllo = I check
• tu controlli = you check
• lui/lei controlla = he/she checks
• loro controllano = they check

Since the subject is due escursionisti = two hikers, the verb has to be plural:

• Due escursionisti controllano... = Two hikers check...

This is normal subject-verb agreement.

Not usually. In this sentence, controllare means to check, to inspect, or to monitor.

That is a very common point of confusion for English speakers, because it looks like to control, but often means something closer to:

• check
• verify
• inspect
• monitor

So here:

• controllano il dislivello e l'altitudine = they check the elevation difference and the altitude

Sometimes controllare can mean to control in certain contexts, but to check is often the more common everyday meaning.

This is about gender and articles.

• dislivello is a masculine singular noun, so it takes il
• altitudine is a feminine singular noun, and because it begins with a vowel, la becomes l'

So:

• il dislivello
• l'altitudine = short for la altitudine, but Italian does not keep la before a vowel; it contracts to l'

This is very common:

• l'amica = the female friend
• l'acqua = the water
• l'altitudine = the altitude

They are related, but not the same.

• altitudine = altitude, the height of a place above sea level
• dislivello = the difference in elevation between two points; in hiking, it often refers to elevation gain or vertical drop, depending on context

So if hikers are planning or checking a route:

• altitudine tells you how high you are
• dislivello tells you how much you go up or down

This is why both words can appear together in a hiking context.

They are singular because the hikers are checking the elevation difference and the altitude as concepts or specific measurements, not multiple separate ones.

Italian works the same way English does here:

• Two hikers check the elevation difference and the altitude

Even though the subject is plural, the objects do not have to be plural. The number of the noun depends on what is being referred to.

If there were several altitude readings or several elevation differences, then plural forms could appear:

• i dislivelli
• le altitudini

But in this sentence, singular is the natural choice.

Because these are two separate nouns, and each one normally keeps its own article.

• il dislivello
• l'altitudine

When joined by e = and, Italian often keeps the article with each noun, especially when the nouns have different genders or different article forms.

So:

• il dislivello e l'altitudine = natural and correct

Repeating the article makes the structure clear and sounds normal.

Yes. This is a very standard subject + verb + object order:

• Due escursionisti = subject
• controllano = verb
• il dislivello e l'altitudine = object

Italian often allows more flexibility than English, but this order is the most neutral and straightforward.

So this sentence sounds natural and unmarked:

• Due escursionisti controllano il dislivello e l'altitudine.

You could change the order in some contexts for emphasis, but this version is the plain, standard one.

The apostrophe shows that the article has been shortened before a vowel.

• la altitudine is not used
• instead, Italian uses l'altitudine

This shortening is called elision.

It happens with singular articles before vowel sounds:

• l'amico from lo amico in modern standard usage
• l'amica from la amica
• l'altitudine from la altitudine

So the apostrophe is not optional here; it is the normal correct spelling.

The main change would be the noun for hikers:

• Due escursioniste controllano il dislivello e l'altitudine.

Why?

• escursioniste = feminine plural
• controllano stays the same, because the verb form for they is the same whether the group is masculine or feminine

So:

• due escursionisti = two male hikers or a mixed group
• due escursioniste = two female hikers

The ending -isti is the masculine plural ending for many nouns in -ista.

So:

• singular: escursionista
• plural: escursionisti

This pattern is very common:

• turista → turisti
• artista → artisti
• ciclista → ciclisti

For pronunciation, a rough guide is:

• escursionisti ≈ eh-skur-tsyoh-NEE-stee

The sc before u sounds like sk, and the stress falls on ni:

• escur-sio-NI-sti

This kind of noun pattern is worth learning because it appears often in Italian.