This works:
if exist %1\* echo Directory
Works with directory names that contains spaces:
C:\>if exist "c:\Program Files\*" echo Directory
Directory
Note that the quotes are necessary if the directory contains spaces:
C:\>if exist c:\Program Files\* echo Directory
Can also be expressed as:
C:\>SET D="C:\Program Files"
C:\>if exist %D%\* echo Directory
Directory
This is safe to try at home, kids!