User blog comment:Solowing106/Tunnels/@comment-4196571-20120801155711

Well, I have only played 4, 5, X, and X2 and I would say Archelon fortress is the hardest as the end of the tunnel zooms straight up and the whole area shakes. Plus, it is extremely hard to fly through the tunnels to kill Fenrir if you don't immedietly kill him with missiles or a TLS.