web server behind a router

I wanted to test the access to my web server, not with the http://localhost adress, but with the WAN adress provided by my ISP.
I set port forwarding in the router: to the port 80. But still couldn't access the files. It's because of a Lan loopback problem. Or something like that.

I had to use a proxy server instead. Search on wikipedia if you want a list of available proxies. Then with a Danish anonymus proxy, changing the browser settings to use that proxy, I could see that my site was reachable from the outside.