Learn Turkish: Raylar sahil boyunca devam ediyor. - The rails continue along the coast.

Boyunca is a postposition that attaches directly to a bare noun (a noun with no case endings) when referring to a continuous extent of space or time. That is why it is simply sahil boyunca (along the coast) rather than taking a locative or dative case.

Where does the word boyunca come from?

It is built from the noun boy (length). It takes the third-person possessive suffix -u, a buffer letter -n-, and the adverbial suffix -ca (meaning 'measuring' or 'in the manner of'). So sahil boyunca literally means 'by the length of the coast'.

Can boyunca also be used for time instead of physical places like the coast?

Yes! Just as it means 'along' for physical space in this sentence, it means 'throughout' or 'during' for time. For instance, yıl boyunca means 'all year long' or 'throughout the year'.

Why is the verb devam ediyor two words?

It is a compound verb consisting of the noun devam (continuation) and the helper verb etmek (to do or make), conjugated here in the present continuous tense (-iyor). Turkish frequently uses etmek with borrowed nouns to turn them into action verbs.