The woman who came to the door left flowers for you.

Tik Tok, which I find useless, is from China.

Is this what you were talking about?

She finally visited the coffee shop that had such great reviews.

*****

She apologized to the boy whose glasses got broken.

The house whose owner is on vacation has an unsightly garden.

The house, the owner of which is on vacation, has an unsightly garden. (This is correct but less used.)

*****

She decided to move to London, which surprised me.