If you don´t found the bar, you have to go to Plaza del Tossal (search in Google) and ask someone how to go to the Immortal, it´s very near.

I also didn't find this bar on my first try (during the day). When I asked some metalheads for a good metal bar, they suggested this one and to my surprise it really is at this address. There is just no sign on the outside.
Inside, beer is pretty cheap (Estrell Damm for 2 Euro). Unfortunately I went there on a day when they didn't play much music, because there was some strange auction going on, where girls could bet for the local metalheads to take their shirt off.
So, after a while I left the bar and headed over to the La Flama.
The bar is located in the center of the city, it's better to have a map, as the streets are small and you can easily loose orientation (especially after a few beers).
You can also get "Immortal metal-bar" t-shirts there for 8 Euros.
Was okay, but I would have preferred to actually listen to some more music instead of this strip show...