Learn Spanish (Latin America): Nosotros volvemos a dormir en el hotel.

In Spanish, stem-changing verbs like volver (to return) do not change their stem in the nosotros (we) form. So, the 'o' stays as an 'o', giving us volvemos. If it were 'he returns', the stem would change to él vuelve.

Since dormir is also an 'o to ue' verb, why isn't it changing here?

Because dormir is in its infinitive (unchanged) form here, meaning 'to sleep'. You only apply stem changes when you conjugate the verb to match a person (like yo duermo for 'I sleep'). In this sentence, volvemos is the conjugated verb, and dormir just follows it.

Why do we need the word a between volvemos and dormir?

Verbs of motion or direction (like going, coming, or returning) usually require the preposition a before a following infinitive verb. So, volver a dormir translates to 'to return to sleep'. As a fun bonus, the phrase volver a followed by an action can also mean to do that action again (e.g., 'we sleep again').

Why use en for 'in the hotel' instead of a?