sudo aptitude install encfs
sudo addgroup <user_name> fuse  # make sure your user is allowed to use fuse
 
# Note that you may need to re-login before you are recognized as member of the "fuse" group

# create directory for encrypted data and a mount point
mkdir /mnt/data/data.crypt   # the directory with the encrypted data
mkdir /home/user/data        # the mount point
 
# initialize/open the encrypted directory
encfs  /mnt/data/data.crypt /home/user/data  # enter 'p' for paranoia mode and choose a password
 
# now copy your super-secret stuff to /home/user/data
 
# when finished
sudo umount /home/user/data 

Notes:

• encfs DEMANDS absolute paths, otherwise it will not work
• encfs DEMANDS that the mountpoint be empty, otherwise it shows an error message