Learn Russian: Обмен валюты работает круглые сутки. - The currency exchange is open around the clock.

In Russian, it is standard to use the verb работать (to work) to say that a shop, service, or institution is open or operating. For example, if a store is closed, you would say it doesn't work (не работает).

Why is the word валюты in the genitive case?

The noun обмен means "exchange." We put валюта (currency) in the genitive case to link the two nouns, literally creating the phrase "exchange of currency."

The translation says "around the clock," but what does круглые сутки literally mean?

It literally means "round 24-hour periods." The noun сутки means a full 24-hour cycle of day and night. It is a word that only ever exists in the plural form, which is why the adjective круглые (round) is also plural.

What grammatical case is the phrase круглые сутки in, and why?

It is in the accusative case. In Russian, when you state how long an action lasts (the duration of time), you put the time phrase directly into the accusative case without using a preposition.