CryptoFS is a encrypted filesystem for Filesystem in Userspace (FUSE) 
and the Linux Userland FileSystem (LUFS). 

CryptoFS will use a normal directory to store files encrypted. The 
mountpoint will contain the decrypted files. Every file stored in 
this mountpoint will be written encrypted (data and filename) to the 
directory that was mounted. If you unmount the directory the encrypted 
data can only be access by mounting the directory with the correct key 
again. Like other FUSE/LUFS filesystems it does not need root access 
or any complicated setup like creating a filesystem on a encrypted disk 
using the loop device.

This requires fuse (also available at SlackBuilds.org), although it can 
alternatively use LUFS if you have that installed from elsewhere.