Questions & Answers about Idziemy do muzeum mniej więcej godzinę.
It is grammatically correct and understandable. A Pole will know what you mean.
However, depending on what you want to say, a native speaker might choose slightly different, more typical phrasing:
- For “we (will) walk to the museum, it takes about an hour”:
- Idziemy do muzeum przez mniej więcej godzinę.
- Do muzeum idzie się mniej więcej godzinę.
- Droga do muzeum zajmuje mniej więcej godzinę.
Your sentence is fine as a learning example, just be aware that other versions are often more idiomatic.
After the preposition do you always use the genitive case.
- do + genitive:
- do sklepu (from sklep)
- do domu (from dom)
- do szkoły (from szkoła)
- do muzeum (from muzeum)
The noun muzeum happens to have the same form in several singular cases (nominative, accusative, genitive, etc.), so you cannot see the genitive ending in the form itself. You know it’s genitive only because of the preposition do.