Is there an admission fee?

There is no admission fee to world trade center itself but there is an admission fee to the museum and the observatory.

No

The One World Observatory standard ticket costs 34$ (https://owo.secure.accesso.com/subKeyword/Guest%20Admission?keyword=Guest%2520Admission). The memorial & museum costs 24$ (https://www.911memorial.org/visit-museum-1).