Redirect direct access to subfolder

[thodorisgo]

Hello.
On my host root i have my main website and there are also some subfolders with some other sites aswell that are related with their own domain names.
I'm looking for a way to block the direct access to those subfolders maybe with a redirect for example www.mainsite.com/othersite to redirect to www.mainsite.com.
Is there a code that i can add to my htaccess file to make this work?

Kind regards

[Per Yngve Berg]

Create the sites as siblings instead of sub-folders.

[gws]

You can password protect directories on the server cpanel.