On the bash prompt one, three or more slashes (/,///,////, ...) are treated as a single slash, whereas two slashes (//) are left as is:
12:07 $ cd /
12:07 $ pwd
/
12:07 $ cd //
12:07 $ pwd
//
12:07 $ ls
bin boot cdrom dev etc home initrd.img lib lib64 lost+found media mnt opt proc root run sbin srv sys tmp usr var vmlinuz
12:07 $ cd ///
12:07 $ pwd
/
12:07 $ ls
bin boot cdrom dev etc home initrd.img lib lib64 lost+found media mnt opt proc root run sbin srv sys tmp usr var vmlinuz
Usual suspects' versions:
12:07 $ bash --version
GNU bash, version 4.3.11(1)-release (x86_64-pc-linux-gnu)
12:20 $ dpkg-query -s coreutils | grep Version
Version: 8.21-1ubuntu5