Cities of Death

This. And even more terrain in form of ruins. All that glorious 4+ cover!!

Cities of Death is an expansion for Warhammer 40,000, published by Games Workshop in 2006. Its theme is urban combat, as opposed to the relatively sparse terrain of typical Warhammer 40,000 battles. It has also become a completely new way of playing W40k, because of the recent rule-book editions favoring the shooting phase more. Some armies naturally benefit more from a heavily dense terrain maps, but that should not stop people from coming up with creative ways of balancing out the games, by adding homebrew rules. Like deciding one half of the terrain being dangerous, to help, but at the same time inhibit the an assaulty army.

Besides that, the featured guidelines for setting up dense terrain (not so close that nobody can fit anywhere, while staying close enough together to restrict movement and lines of sight -- generally two to six inches), are included together with rules for moving and fighting inside terrain, "stratagems" that could be employed by armies to represent strategies or assets used by armies specializing in urban combat, and new mission rules for city fights.

The rules for moving and fighting in terrain were mostly folded into the main rules in Fifth Edition, while some of the stratagems are outdated by rules changes or superseded by Sixth Edition's "warlord traits". At least the advice on modeling dense cities is still pretty good.