Learn German: Wann willst du das Museum besuchen? - When do you want to visit the museum?

willst comes from the German verb wollen, which means 'to want' or 'to intend to'. It is a classic false friend! Even though it looks like the English future tense word 'will', it actually expresses intention or desire. Here it is conjugated for the informal 'you' (du).

Why is the action verb besuchen (to visit) placed at the very end of the sentence?

This is a strict word order rule in German when using modal verbs like wollen. The conjugated modal verb (willst) takes the standard verb position right after the question word (Wann), and the main action verb (besuchen) gets pushed to the very end of the sentence in its original, unconjugated dictionary form (the infinitive).

Why is it das Museum instead of den Museum if it is the direct object being visited?

Museum is a neuter noun, so its word for 'the' is das. In German, only masculine nouns change their 'the' (from der to den) when they are the direct object of an action (the accusative case). Neuter (das) and feminine (die) nouns look exactly the same here as they do when they are the subject of a sentence.

How would this sentence change if I were asking someone formally?