Learn Hardcore Polish: Podróżnik wysyła kolejne zdjęcie wieży razem z krótkim opisem w każdym miesiącu. - The traveler sends another photo of the tower along with a short description every month.

Because wieży describes what the photo is of. In Polish, the noun zdjęcie (photo) is followed by czego (genitive) to answer “photo of what?” So you say zdjęcie czego? → wieży, putting wieża into the genitive case.

How do I know to use the instrumental case with krótkim opisem?

The preposition z (with) always takes the instrumental case when indicating accompaniment. Thus z krótkim opisem means “with a short description,” using the instrumental singular of krótki opis → krótkim opisem.

What case does w każdym miesiącu use, and why?

The preposition w meaning “in/during” requires the locative case when talking about time periods. Miesiąc (month) becomes miesiącu in the locative singular, and każdy (every) changes to każdym, giving w każdym miesiącu (“in every month”).

Could I say co miesiąc or każdego miesiąca instead of w każdym miesiącu?

Yes. All three express the same idea:

co miesiąc is more colloquial and concise.
każdego miesiąca uses the genitive after expressing frequency.
w każdym miesiącu uses the locative.
Choose based on style and rhythm; they are interchangeable in most contexts.

Why is the verb wysyła in the present tense when the action repeats each month?

In Polish, the present tense covers both current and habitual actions—just like English simple present (“he sends”). There’s no separate habitual aspect, so wysyła perfectly conveys the monthly repetition.

What part of the sentence is the direct object, and what case is it in?

The direct object is kolejne zdjęcie. It answers co? (what?), so it’s in the accusative. Since zdjęcie is neuter, its accusative form is identical to the nominative. The adjective kolejne agrees in case, number, and gender (accusative neuter singular).

Why is kolejne used here instead of następne or każde?

Kolejne highlights the ongoing sequence—each successive photo in the series.
Następne often refers to the very next one rather than the entire continuing series.
Każde simply means “every” or “each” without stressing order.
Thus kolejne zdjęcie underlines that these photos form a continuing sequence.

The word order seems flexible. Could I start with W każdym miesiącu instead of Podróżnik?

Absolutely. Polish word order is free because cases show grammatical roles.
W każdym miesiącu podróżnik wysyła… is just as correct and puts more emphasis on the time. The original word order (subject–verb–object) is neutral and very common.