관계사 문제 질문드려요

문장에 들어갈 관계사가 헷갈려 질문드려요.

(where, what, which) makes Namdaemun fascinating is its stores (where, that, when) specialize in only one item, such as umbrellas, belts, gonseng or towels.
앞 괄호에는 어떤 말이 들어가나요? 뒤 괄호는 목적어 유무로 구별하는 건가요? stores 뒤라서 where일 것 같은데 잘 모르겠어요.

(what, that, which) is important is (what, that, which) you need decide what is best for you.
앞 괄호와 뒤 괄호에는 각각 무엇이 맞나요? 뒤에는 선행사가 없어서 what인지 궁금합니다.
There are a few cases (where, which, how) this rule does not apply.