Ok Here goes.
Map 2: Spacestation 13
Map 3: DeadBridge
Map 4: Frostbite.
Here's a description for ruins:
You wake up in a small basement, two windows... Easy peasy. After some time, you open the door and gain another 2 windows... but you get a trench gun! Still easy. THen you get a choice... Upstairs or into a smaller side building? Whatever your choice, you end up outside! You still must fight against the growing amounts of zombies though! After that you pass through a single building... and end up in a massive temple!