go to robots.txt http://natas3.natas.labs.overthewire.org/robots.txt then, go to the secret dir: /s3cr3t/ there you can find the password in the url: http://natas3.natas.labs.overthewire.org//s3cr3t/users.txt
Flag: QryZXc2e0zahULdHrtHxzyYkj59kUxLQ
QryZXc2e0zahULdHrtHxzyYkj59kUxLQ