This mission is about the settings on Apache server by .htaccess file that defines the files and the directories are available and visible to the external visitors. You might see more info about .htaccess.
Now when you open the mission you will se some song names going around for each refresh. Search the musics on google and you notice that all the songs are related to Elton John. Is this a coincidence. I don't thin so :). In addition if you look the forum on hackthissite about the mission they give some clues. By depending on these tips try to go /e/l/t/o/n url added to main address of the page. You see that there is no file there after /n. So it is time to see the htaccess file. By the assumption of we have the file here, type .../.htaccess to the url. You will see that two of file is prevented to be shown on file three but we can actually see them. One of the file is DaAnswer. Delete /.htaccess and type /DaAnswer. It says something tricky. "... answer is ---- ...". The answer is lying there ---- part. Copy the word lying instead of ---- and go back to /mission/11/index.php and type this word as a password then you pass the mission.