Redirecting to default page when trying to access folder

Hello,

I'm working on a project which includes a lot of web pages. The web pages are grouped into folders depending on some criteria, for example:

User:
- Registration
- PersonalData
- RecentActivities

Administrator:
- Login
- ListUsers
- OtherStuff

I access to a page using the link: http://localhost/User/Registration.aspx or http://localhost/Administrator/Login.aspx and its ok, but when I insert http://localhost/User it returns me the list of files included in this folder. I want to prevent this! I would like that when I try to enter the folder it returns me by default to the Login page.