Why can bash cd to //?
From the Bash FAQ:
E10) Why does `cd //' leave $PWD as `//'?
POSIX.2, in its description of `cd', says that three or more leading slashes may be replaced with a single slash when canonicalizing the current working directory.
This is, I presume, for historical compatibility. Certain versions of Unix, and early network file systems, used paths of the form //hostname/path to access `path' on server `hostname'.