In theory, the Millwall anthem "Let em all come down to the Den" had to be rewritten into "Let em all come down to the New Den". The "Old Den" is history, instead the club moved to the "New Den", which was built a couple of hundred meters from the old location. As the Millwall anthem is good as it is, the club decided to change the name of the new stadium back to "The Den" (well, not only because of that...).
Anyways, the (new) Den is a fairly new ground, which features identical two-tierd stands behind the goals and along the sidelines. Although it misses the hostile atmosphere of the old ground, the industrial surroundings of the new ground and massive presence of police don't really make you feel welcome. Still it's safe to visit a match there.
The home of the Millwall fans is Cold Blow Lane Stand, which seems a bit strange as Cold Blow Lane is more than 500 meters away from the new ground. Again, the club brought the name over from the old ground, not only because it says "Saturday, Cold Blow Lane, we've all come down to cheer" in the club anthem.