Learn Turkish: Onlar bugün denize gitmiyor. - They are not going to the sea today.

The -e is the dative case suffix, which means to or towards. Since the verb gitmek (to go) involves movement to a destination, we add this suffix to the destination noun. Following e-type vowel harmony, deniz takes -e, making denize (to the sea).

Earlier I learned that going is gidiyor. Why does the verb keep a t in gitmiyor?

The root of the verb is git-. Normally, when adding a suffix that starts with a vowel (like -iyor), the t softens to a d (making gidiyor). However, because the negative suffix in this sentence starts with a consonant (m), the t does not change.

Where does the negative meaning come from in gitmiyor?

The negative meaning comes from the -mi- right before the -yor suffix. The standard negative suffix for this verb is -me, but when the present continuous suffix -yor is attached, the e narrows to an i. This makes the word gitmiyor instead of gitmeyor.

Could I change the word order and say Bugün onlar denize gitmiyor?

Yes! Turkish word order is flexible, though the verb almost always stays at the end. Time words like bugün (today) often go near the beginning. By keeping denize immediately before the verb, you are giving the destination the main emphasis in the sentence.