1. In your first example you are saying that you have never been a museum. Since you are a human being, that sentence may be grammatical, but it does not make any sense. In sentences such as the ones you are referring to, it is always necessary to use a preposition of location to avoid the above mistake.
You haven't been a museum, you've been to a museum.
2. Prepositions should be used to introduce prepositional phrases. Therefore
"...back to [the] town where I was born," is a far better construction than
"...back to [the] town I was born in," even though better [paid] writers than I end sentences with prepositions all the time.
3. My uncle, about whom you know llittle, has just sent me this telegram.
Good luck with your studies.